Okay, I'm not one to worry much about the "Face against the chamber" issues with
most bullpup designs.
But when all that's between my cheek and the chamber is just your standard AK/AKM sheetmetal dustcover... PROBLEM!
Oh, and Hoplophile, unless it absolutely HAS to be 9mm, if you really just want to play with the concept of sub-sonic high sectional density rifle cartridges, the .300 whisper is right up your alley. I think the .300 whisper AR uppers might not be in production anymore, but I think they can still be had made to order, or there's stock left to be sold. Or a good AR smith can make you one, all that's needed is a .308 barrel, with the hybrid .223/5.56x45 chamber reamer for the .30 caliber bullet.
There's loading dies to be had, and the .223 brass and various .30 bullets are as common as can be.
Even if it's 100% custom AR upper work, with $200 NFA for a supressor, and the suppressor, and an AR lower if you don't already have one, the whole thing can be done cheaper than importing a VSS Vintorez eve assuming you were allowed to do so.
If it HAS to be 9mm, (.357 hunting projectiles for safari rifles?) somebody would probably be willing to make you the reamer and dies, and could use an AR-10 & bolt to use a .308/7.62NATO case-head as the starting point, and a 9mm barrel blank for the upper.