The best places to buy plants, etc. is from other aquatic gardeners, for example at: The Planted Tank Forum or at: Aquatic Plant Central- aquascaping...a living art
You can "advertise" for Nerite snails there, and if anyone has any for sale you will almost always get a good price and good quality, with low cost shipping.
Not really, I was not impressed by the snails personally, I had 200 of them also.
Some folks make claims, I'd try and get the African zerba shell types personally if you can.
The same genus name confused some folks into beliving these are the same.
I got mine directly from the rivers in both coasts of Mexico, I have about 200 in my 565 gal aquarium, I think they are an excellent algae control,
thanks,
Melo