Fish Markets in New Bedford
It is S New England board. As a non-local here are a few places I have gone.
Fleet's Fisherman's Market is probably a good option and something nice (aside from the fact they land their own fish) is they post availability and prices including whole fish -- just :
Amaral Fish Market for a Portuguese market (overall) and fishmonger.
Also Kyler's Katch
If you are picking up supplies it would be worth a trip to Sid Wainer's Gourmet Market, but not necessarily for fish.