I'm awaiting an answer from a R2R moderator at the moment. I want to make sure I can post a sufficient answer and stay within the guidelines of R2R. I'llhave you an answer soon though.
For nassiurius (or however you spell it) snails, go on ebay and check there. You can get 300 for 30$ (they also have smaller lots). No company can come close to that price.
I bought some on there a couple years ago...probably have about 2 left. They're some odd variety or something. I have NEVER seen any of them go under the sand. They stayed on the rocks and glass.
I bought a clean up crew about a year agi and ive been very happy I got them from a reputable side that sells pre made kits per tank size. Dont know if I can say the name on here but its the same people mr salt water tank uses pm me and ill send you a link