Welcome to the group Serpinski. As Gene said, check the thread he linked to for more information about getting a group order of SouthDown sand.

There's a guy i've talked to that lives close to S. Padre island whol mentioned he finds all sorts of snails and shrimps off the coast which he uses in his tank. I'd be a little weary of using actual sand from the beaches though... there's no telling what pollution you'll bring back to your tank.

8)