Hi David,
Asside from forum members ( and Ed Tinker i selling quite a lot of very nice pieces right now), the two bigger dealers I would recommend, especially for a beginning collector, are FGS and Simpsons. You will pay a premium for their items, but they are knowlegable, stand behind their items, and I have never heard of anyone who has had a bad experience with them re authenticity of a pistol, that they did not rectify. A search on both this and Jan Still's site will give you some feedback on most of the dealers out there.
http://www.fgsfirearms.com/
http://www.simpsonltd.com/
Good Luck,
Vince