Where can I buy a Syrinx aruanus or other large snail for my fresh water aquarium?

I would really like to get a large snail for my aquarium, but have yet to find one that is over an inch or two long/diameter. I think that the Syrinx aruanus is supposed to be the biggest, but I don't know if it can live in a 20 gallon freshwater tank (with only one betta fish no less). Major thanks for all and any help!|||Syrinx aruanus is a SEAshell. It won't live in freshwater. Also these grow to 20" or more so a 20 gallon would be out of the question! And last the SHELLS are from $50 to $280 or more! If you want a large snail, try an apple snail. They get pretty big (hence the name) and are cheap. You can find them about any where. They will eat the algae in your tank too.