I know that FishHeads on LBI only has Frozen Clams this week,they open up a 8AM but you might want to check in with them before that to see if any boats got out during the week and delivered some freash.Here is their 3 609-494-5739.
The clam dealer at the back end of Berlin Farmer's Market sells bags of large (3") clams just as cheap as bait shops or cheaper.
I think they are open 7-days a week but I don't know the hours. I buy bags for chum and bait out on the wrecks and they work just fine. Tougher to open than surf clams tho.