Games Workshop has a lot, but they are a bit too comic for my tastes. Then again, you're talking about putting dragons on a model railroad.
Check out Reaper miniatures at www.reapermini.com and Iron Wind at www.ironwindmetals.com as well as others. Keep in mind that these are all unpainted, and in the case of dragons will usually need to be assembled as well. They may be white metal, plastic, or both. Be prepared to use your pin vise to drill holes to pin the wings and tails on for durability.
There are a lot of other companies as well, but these are my current favorites. Iron Wind has the rights to the old Ral Partha minis (also check out www.ralparthaeurope.co.uk - they have the Ral Partha rights in Europe and a few of the available minis are different). These are my favorites (especially Tom Meier's work). Reaper is a newer company with nice detail, although their dragons have the tendency to be more human-like in their anatomy.
Wizards of the Coast (www.wizards.com) who own the Dungeons & Dragons game now also release inexpensive prepainted miniatures, but they are in random packs so you don't know what you'll get in a given box. A lot of gaming stores have individual minis from their sets though and people trade them a lot as well. Some stores (and some of the online stores) open the sets and sell the individual miniatures from these sets. They're also on ebay quite a bit. These are a rubbery plastic but look pretty good, especially if you aren't an experienced painter yourself.
A lot of the dragon minis are scaled a bit small, though. Most gaming minis nowadays are 30mm, or about 30mm for an average human. Different companies measure this differently, (30mm to the eyes or to the top of the head are the common ones). Older minis were 25mm.
Most hobby shops don't carry role-playing stuff anymore. You'll need to find a (relatively) local gaming store. Comic shops often carry stuff as well.
I am actually planning on selling a lot of my old miniatures as well. Let me know what sort of dragon you might be looking for and I'll see what I can do.
Randy
I would recomend games workshop. They have difrent kids of dragons and they are aperantly going to release a brand new kit soon.
Magnus
Are you kidding? There are probably more dragon models around than train models in ALL scales!
If you want cheap, dig through the "What on Earth" catalog. If you want well done, do to Games Workshop and Dixon Miniatures. If you want expensive, head over to Atlanta Cutlery or The Franklin Mint.
I just did a quick Ebay search for "Dragon", and got 50,702 hits. 1971 are in decorative collectables and 2129 are in action figures. You might want to start there to get a feel for what's available.
Ray Breyer
Modeling the NKP's Peoria Division, circa 1943
Check the Squadron Shop online
http://www.squadron.com/
It takes an iron man to play with a toy iron horse.