You can order them online as well, we have actually 3 sets of the now (different speeds) for aquarium servicing. They work GREAT on fake coral inserts (not that any of you would have that!).
I have tried them a tiny bit on GSP, only where it was about to touch something. But they sure do slime when you do it, so only recommended small portions plus the addition of carbon to the tank.
Same goes for the Anthelia, but I've nuked quite a bit at one time with no ill effect.
Cheers
-Diana