Viet Hoa supermarket is the place to get live blue crabs lately. I thought the 99-cents-a-pound price was a limited time special, but regulars tell me blue crab has been 99 cents/pound at Viet Hoa for awhile now. The thing is, when you walk up to the crab counter, most of the crabs are either tiny or dead. There is some strategy involved, especially on Saturday morning.
You have to get into position and wait until the seafood guy comes out with a new crate. First, he picks through the mess on the table to get each and every live crab out. Then shoves the dead ones into a bin for processing. Finally, he dumps a new box of live crabs out and the crowd plays dueling tongs to get the biggest ones. The fresh crabs are hard to catch -- they grab hold of the tongs and each other to avoid capture.
It took me a while, but I ended up with a big bag of crabs for $7.