El Tablon
I can't give you exact directions, but if you enter Charamicos and head toward the ocean, you can find the beach of El Tablon. This is where the local fisherman come in with their catch and they have a co-op right on the beach where all manner of seafood is sold according to the daily catch. Anyone can buy there. I understand that it's very crowded early in the AM, but they have refrigeration at the coop and at about 3:00PM one afternoon I was offered fresh tuna and lobsters (a lucky day) along with the usual fare. Don't recall exactly now, but the prices struck me as quite reasonable at the time.