Hi Butch,
There is a fish market and restaurant in Aguada called . It's a bit difficult to find, but our neighbors bought fresh Mahi Mahi from them and it was delicious...about $7-10/pound I think.
There is also a on Saturdays in Aguadilla, but I haven't been there, as the one in Rincon is closer to us.
Good luck finding them, and please let us know how it goes! 