RE: I have a D&RGW coat
Probably a small market for it. But there are at least a few avid fans of the RR that would be interested. As is usual, e-bay (or one of the other online auction places) is probably the best way to reach the widest audience. I assume there is a "friends" organization for the place and they probably have a web presence and probably have a forum that you might be able to advertise on. A search of the web would reveal them. Of course, you probably would need to know about what price range you want for it... and that is probably why you asked here!
What kind of coat is it? A good leather jacket can get $200 or more, retail. A Wal*Mart cloth winter coat would be less than $50, even with some sports logo on it. You will need to supply some photos of it. If you join this site you can post for sale items and I think this would fit the general classification of what is allowed to be sold here (but NOT my decision about that, check with Shad, the forum owner).
Do a search of e-bay to see if you can find similar products, that would give you some idea of price... and it could put dollar signs in your eyes or severely disappoint you!