I've seen ads for "Dwarf Giant Salamanders" lately. They seem to be a number of different common salamanders. I've never heard of anyone keeping this other than some very old specimens in China.
You used to be able to get hellbenders which are pretty darn cool though not as big. I think the laws have changed though as I have not seen any available in years.
They are a totally protected species. They are considered a "monument" species. Meaning, the salamanders themselves and their habitat are protected. They are rare, their numbers are declining due to habitat loss as well as disease brought on by agricultural chemicals.