Mike, when I did that I ordered shucked fully belly clams from Maine. I had a couple wholesalers saved in my favorites so I posted them for you. Both are pretty pricey, but I just had to have them one time after reading some clam threads on RoadFood. The Ipswich clams from Massachusetts are supposed to be the best, but I couldn't justify the cost. I ordered the Maine clams from the second link.
It was funny, when I ordered them, I told the guy what the price was for the Ipswich and he burst out laughing. Obviously he felt the Maine were comparable. I ordered five quarts to defray the shipping cost and froze some of them. They weren't as good after being frozen for a while, but what seafood is? I actually through one quart out after it was freezer burned when I opened it.
Anywhooo, was it worth the price? My wife was a little crabby about it, but I thought it was fun. She doesn't like seafood quite as much I do.
I will say that those clams were a heck of a lot better than lobsters we ordered from Legal Seafood out of Boston with a gift certificate we received once as a gift. Much better to buy those out of the tank from the local Sendik's market.MA Ipswich ClamsFull Belly Clams From Maine