If you go down to the fish market by Chinatown, Grand Street to Mulberry street, you'll see that they have all sizes of shrimp. Now it's not mysis shrimp but it's just as good.
You would be surprised at what you'll find at the fish markets down there, once they had 7" Mantis shrimp, gray in color. They also had live shrimp, they looked like peppermint shrimp, but they where very large about 2" high and 6" long. I don't know how they would have done in a reef tank but the tank had to be very large because they where really big. They where going for $14@lb.