you mean a full auto AR pistol ?
(I've never enjoyed the semantic debate over whether a gun is an M-16 or an AR -15... to me, an AR with an Auto sear is an M-16...)
What you would need to do is buy ANY AR pistol (patriot or other) and then buy a legal registered Auto Sear or Registered FA lower and attach it to the Pistol upper.
If it were me, and I've owned An AR pistol, I'd much rather have a FA AR-15/M-16 with a short barrel and a collabsible or folding stock of some kind.
I seriously thought about getting a legal SB (8 inch) AR this year, but decided not to invest the money. If I had done it, I was going to look into buying a registered Auto sear and a suppressor as well over the next year or so, so the whole project would've been close to $4000.