Where to start?
The obvious answer for where to start when getting yourself a Space Marine epic force is with the basics: HQ and Troops. It turns out, those are available in abundance on Ebay. The command squads often contain chaplains, techmarines, librarians, as well as captains, and if you are willing to spend 20-30 bucks you can get a bunch of infantry models, often a good mix. In fact if you can find them on sprue the plastic infantry for SM include scouts, tacticals, techmarines, librarians, terminators, captains and even bikes! My first step was to look for such a deal, and they are out there. Once you have the core of your force, you will notice that there is a great deal of variation between what is abundant (and cheap) and what is rare (and expensive). What follows is my best attempt to guide you to all the best 3rd party proxies for 6mm Space Marines.
The Definitive Guide to Epic Scale Space Marines and Proxies
I. HQ
II. Troops
III. Dedicated Transports
IV. Elites
V. Fast Attack
VI. Heavy Support
I. HQ
These models are just plain easy to find on ebay, and frankly Marine style models are not common among 3rd party sellers. I will list the 1-2 ones that are available in the Troops section.
Special Characters: To get these WYSIWY, you will need to do some serious converting
Captain: eBay "Epic Command Squad"
Bike Captain: Use a Space Marine Bike
Terminator Captain: Use a Terminator
Librarian: eBay "Epic Command Squad"
Techmarine/MoTF: eBay "Epic Command Squad"
Chaplain: eBay "Epic Command Squad"
Apothecary: eBay "Epic Command Squad"
Command Squad: eBay "Epic Command Squad"
Servitors:
II. Troops
Similar to the HQ's for Space Marines, you should be able to find tactical and scout marines on ebay pretty easily. You might have to watch for a week or two to see a decent deal pop up, I wouldn't jump in right away unless you see a good deal.
A. Tactical Marines
B. Scouts
A. Tactical Marines
Really, I recommend getting them on ebay. The options that are out there just don't look very good but, nonetheless here's what I could find:
B. Scouts
Scouts tend to be readily available, but if you're looking for 3rd parties, there are a few options. If you intend to do WYSIWYG 3rd parties or conversion are your options for sniper scouts.
Guild Myrmidon Centuria seem to make decent scouts, they come equipped with a wide variety of weapons
III. Dedicated Transports
A. Rhino
B. Razorback
C. Drop Pod
D. Land Speeder Storm
A. Rhino
Rhinos are available in mass quantities on ebay, but if you feel the urge to use a 3rd party, there are a ton of APC options
B. Razorback
The Razorback is a venerable transport, but its models on ebay are surprisingly expensive. They are a simple conversion from a rhino (which are abundant and cheap), and if you aren't interested in getting your hands dirty, Shapeways delivers:
C. Drop Pod
Drop Pods are actually somewhat difficult to find on ebay, at least at a price point I am willing to pay. There are more of the old style pods, which don't resemble modern drop pods at all, but there are thankfully several 3rd party options
D. Land Speeder Storm
There wasn't a Land Speeder Storm back in the day, so you have to make due with a Land Speeder model generally. The other option is to use one of the mediocre 3rd party stand-ins. You can pretty much use anything in the Land Speeder section as well.
The Buggy model could make a decent LS Storm with some alteration (like removing the wheels obviously)
IV. Elites
A. Vanguard Veterans
B. Sternguard Veterans
C. Dreadnought/Ironclad
D. Legion of the Damned
E. Terminators
F. Centurion Assault Squad
A. Vanguard Veterans
Vanguard Veterans are essentially marines or assault marines, depending on whether they have jump packs, I would recommend using Assault Marines and painting them differently.
B. Sternguard Veterans
Similar to Vanguard, Sternguard are an elite version of the standard tactical marine, so you can use anything from the Tacticals section and simply use a different paint scheme to differentiate.
C. Dreadnought/Ironclad
Dreadnoughts are available in decent quantities on eBay, but the style and variety are limited, especially what is broadly available
Contemptor Dreadnoughts are another option that are available in big numbers on ebay. There is also a proxy option for them:
D. Legion of the Damned
Legion of the Damned are once again easily made using Tactical Marines, but if you are looking to make them stand out, I can recommend using a skeleton in 6mm scale to swap heads.
E. Terminators
Terminators are fairly easy to find on eBay, and really aren't expensive. The only trouble is that they aren't available with close combat weapons. As a result, you will need to do conversions to get them WYSIWYG. I really can't recommend any of the 3rd party options for these.
F. Centurion Assault Squad
The Centurion is obviously extremely new, and as a result there aren't really great options for 6mm Centurions. These are going to require conversion. There is one option for a base model though.
V. Fast Attack
A. Assault Squad
B. Land Speeder
C. Storm Talon
D. Bike Squad
E. Attack Bikes
F. Scout Bikes
A. Assault Squad
The humble assault marine is available in decent numbers on eBay, but if you want 3rd party options, there are a couple...
B. Land Speeder
The Land Speeder options on eBay are disapointing, but not nearly as disapointing as the option on 3rd party sites. There are a couple of near misses, but I haven't found anything that quite worked yet.
Microworld Games makes a relatively decent Land Speeder, with a little conversion I think it could work
C. Storm Talon
The Storm Talon was created after Epic finished up, so you're looking at proxies and scratch-builds only
The Khazari Valkyrie is a very similar body to the Storm Talon, with a little trimming it could make a decent Storm Talon
D. Bike Squad
Bikes are available on ebay in abundance, so that's a great starting point. There are a few mediocre bike options, and anything that works for Scout Bikes can work here as well.
E. Attack Bikes
Attack Bikes can be a little harder to find on eBay, but the 3rd party options aren't particularly great either.
F. Scout Bikes
While I don't believe Scout Bikes existed in Epic, there are Imperial Guard bikes that look the part. That said, if you have trouble finding them, there may be options...
VI. Heavy Support
A. Devastators
B. Centurion Devastator Squad
C. Thunder Fire Cannon
D. Predator
E. Whirlwind
F. Vindicator
G. Hunter
H. Stalker
I. Land Raider
J. Storm Raven
A. Devastators
There are a great deal of heavy weapons marines floating around eBay, but if you are looking for devastators and don't want to use ebay, you do have an option:
B. Centurion Devastator Squad
Centurions, as noted above under Assault Centurions, you don't have a lot of options. What you can do is convert terminators, but its going to be some work to get an equivalent model done. Have a look at the 3rd party models in that section for potential conversion options.
C. Thunder Fire Cannon
The Epic Thudd Gun is almost identical to the Thunderfire Cannon, but I have found another option from a 3rd party producer
D. Predator
The Predator is a relatively common sight on ebay, but I have found that prices are a little higher than I'd prefer. If you can't find a good deal on predators, there are a bunch of good options, in fact so many that I'm not going to list all of them, just my favorites. There's also the option of converting Rhinos, which is super simple at this scale.
Another option for Predators is converting a Rhino, for this I would recommend trying your hand with plasticard and greenstuff, but if you are certain you want to buy, Shapeways is the way to go:
E. Whirlwind
The Whirlwind is a pretty easy tank to make from a rhino, and is available on ebay, but if you're looking for alternate options there are a few
The 6mm Whirlwind is an easy conversion, but if you are looking for something truly spectacular looking, Shapeways again comes to the rescue
F. Vindicator
The Vindicator is a great model, and fairly easy to convert or find on ebay, but there really aren't a great selection of alternatives.
G. Hunter
The Hunter is actually originally and Epic model, but finding them on ebay is almost impossible. Still, with a Rhino in hand, it is extremely easy to convert. If you don't want to build it yourself, we have another great option from Shapeways:
H. Stalker
The Stalker tank doesn't really have an Epic scale option, but there is a solid option for a proxy stalker:
The Guild Icharus SPAAG Battery makes a great Stalker, or even better a good source of a conversion bit, as the hobbyist did above
I. Land Raider
I really can't recommend any Land Raider equivalents, you can get Land Raiders cheap on eBay, and the other options are just not really anything like the model, which is the most iconic Space Marine vehicle.
J. Storm Raven
There has never been an Epic scale Storm Raven, but there are a few main options for getting an equivalent model in 6mm. Each has upsides and downsides.
You also have the option of converting one of the newer, more expensive Thunder Hawk models into a Storm Raven. This is going to take some work as it is a pewter model, but there is a great tutorial for doing this
Finally, for the most ambitious (and most budget conscious) There is the option of scratch building the model. This is not for the feint of heart, but it gives you a great looking product if you take your time. Levian on Pocket40k has a really comprehensive tutorial