The Super 88 Market. There are a few through out Boston. One particularly that I KNOW sells shark meat is by my house. It s off of Mass. Ave near the South Bay Mall. Super 88 s are a popular Chinese Market.
Savenor s Market (on Charles Ave, just across from MGH) often has stranger sea foods and meats. (True story- first time I went in there, they were giving away samples of kangaroo jerky.)Make sure you call ahead, though- their products rotate, so not everything is always available.
try a seafood market in Chinatown
C-Mart on Washington Street in Chinatown.
I think if you look around in Chinatown you will find it.
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