How Do I Get Snails To Breed?

[hobbsthepuffer]

I was wondering the best type of snail to keep for breeding, oddly enough. I have 4 figure 8 puffers, and I have heard (and read) that they need snails to trim down the beaks. I cannot for the life of me keep the darn things alive, I have gone to petsmart and picked up the free ones and kept them in a lightly algeaed tank, and the bottom is littered with shells.

If I cant' breed the darn things, where is the cheapest place I cna order them online and still get a quality product? Also, how critical are these critters to my puffers?