As far as I know Petco and Petsmart will never give you anything for free, even if it's dead. (Which I find most of their stock usually is)
I have tons of MTS, all ranging from tiny juvies to full grown adults, I LOVE them, they're the only snails I've found that will sift through the substrate and clean it. Definitely in a niche all their own.
I would mail you some, but they won't survive. It's too cold right now in CA.