the Bristol Farms in So.Pasadena has 2 live chefs and they will do custom if you are willing to wait.It is very decent stuff-but a little expensive. I have never found any other supermarket sushi to be worth going back for.
There is a market in Japantown in LA that makes fantastic sushi-and they move so much of it that it stays"fresh"it is pretty cheap also.
Folks-the whole point of the origin of sushi was preserving fish