According to the Monterey Bay Aquarium, all of these stocks are in good shape (some are farmed). And all are readily available around here.

-Catfish
-Steamer clams
-Mackerel
-Mussels
-Oysters
-Wild Alaskan Salmon
-Sardines
-Striped Bass
-Rainbow Trout

If you extend to include their "good alternative" species, you add things like bluefish, rock bass, porgy/scup, lobster, crabs...

So while it's true that the markets make little-to-no effort to promote these species over less sustainable ones, it's not hard to purchase fish from sustainable fisheries.