sterlets and white sturgeon for sure are legal, if you are near cleveland the rms stores have them for around 30-35 dollars. Do some research before you buy them.
Any sturgeon that is captive bred is possibly legal, local laws can make any sturgeon illegal no matter what and no sturgeon is legal to collect from the wild as a small fish. I've either seen or read about North American native sturgeons like shovelnose, white, and lake being sold in the trade of these only the shovelnose is really suited to captive care by most people. Sterlets are often for sale, they are a European sturgeon.