Well, chico- you have a couple of matters to deal with.
1. The ammo is 9x39mm, a special HEAVY subsonic bullet. I am aware of no commecial sources for it.
2. It is a suppressed firearm, and as such, would have to be registered with the BATFE, and the transfer tax paid.
3. It is a select fire weapon. Unless already registered with the BATFE by May 1986, it cannot be. That was the cutoff date for registering full auto firearms.
Other than that, and do not know if these are even offered on the civilian market, no problems.
What we have here is... failure- to communicate.