Well - there aren't any species of real sharks that live in freshwater fulltime. But there are several that can tolerate freshwater for extended periods - such as the bull Shark. However these species tend to be between 6-12" long, and really aren't suited for anything less than a large Public Aquarium.
The carps & Catfish that are called "sharks" are bony fish, so they aren't real sharks. Just Shark-like in appearance. But generally the most common species found in LFS tend to be Bala Sharks, Redtail Sharks, Columbian sharks (catfish), Black Sharks, and the Iridescent sharks. And they tend to range in max adult size from about 6" to 48".