Also
www.jlaquatics.com and
www.saltwaterconnection.com
BTW, clams are on CITES. That's why you can't order them from the U.S. Well, you can, but you need CITES permits to do it legit. Probably not worthwhile unless your order is about $1000 or so!
CITES is serious business. I just found out a fellow I once did a group order of orchids from, is in jail because he falsified some documents to illegally import some plants into the U.S. (You cannot legally import CITES Appendix II). He was the exporter (from South America). His counterpart in the U.S.,the importer, is also in jail. Both received sentences in the 1.5 to 2 year range. Serious serious serious serious stuff.
I know I sometimes harp on people to not mess with CITES but this was the first time it really hit home for me. It's just not worth it.