I once had a really WHITE white sand but I don't know where it came from...I got it from a friend who was a mason so I think it was some sort of masonry sand. Very very fine and soft and WHITE. Maybe you could call a quarry? I dunno if you have any.
the problem with it was it didn't stay white long. It seemed to age to a very yellow/off white pretty quick. I don't know if this is a problem with all white sands, but it wasn't nearly as attractive as a sand that's just the color of say aroganite to begin with.
oh one other options I've done...I dunno if you have Fred Meyer or any other one-stop shopping equivalent, but in the houseplant section they have little bags of decorative sand that I've used. You have to wash it REALLY good but it's glowing white. you don't get more white. It comes in little bags for like $2.99 each.