well have a tank for just your snails. you can even have it as a lovely planted tank
then supply fish food for them and they'll breed on their own.
just make sure that they have a filter, etc that is cycled
Go to any LFS and ask them for their "Pest" Snails. They should give you some for free, if not, they will be cheap. Then Buy a little tank to put your snails in. Put in an algae wafer and they will MASS produce. Puffers love these.