Gary,
Welcome to Conch-L as well as to shell collecting. Off hand I can't
remember a site that was just for trading. A lot of individuals trade and
even some dealers. If you want to initiate a trade I would suggest a quick
offer of what you have available. An excellent site with a lot of dealers
as well as some offers for shell trades is:
http://www.molluscs.net/index2.htm
Good luck,
Tom Eichhorst in New Mexico, USA