Yes, you can't legally stock it. IIRC, the Contender is the only pistol you can stock, and even then it must have the carbine barrel.
You can find good deals on the Semiauto Cobrays on GunsAmerica. Pistols and carbines.
My buddy has the real deal - a full auto MAC11 - great fun, but way out of my price range - and I don't want to deal with the Federal red tape.
The semiautos often have a trigger slap problem, but I imagine someone has a fix for that?
For my money, there are better 9mm carbines out there.