The Petco at Manchester and Baxter frequently has a variety of nerites. All of mine have died though, except my horned bumblebees and olives. I found that the tracked and zebra nerites tended to flip on their backs and were unable to right themselves. I was constantly flipping them back over, but if I missed them for a couple of days, they died.
I have developed a special fondness for ramshorns, and I keep them in all my tanks now. I even got rid of my assassins so they wouldn't kill off my rams. I throw a couple of handfuls of crushed coral in with my substrate in a lot of my tanks, because it really helps their shells. I have one tank where they have grown huge and range from quarter to dime sized.
My shrimp have stopped breeding. Too much TDS buildup in my tap water. I just bought an RO system and will be installing it today. Once I get things right in all my tanks, I hope they'll start breeding again. You saw my yellow tank. I also have cherries (though most of them died) and BV's. If my colonies get going soon, I'll hook you up.