These guys are located in westfield. They offer gunsmithing services but I don't have experience with them. ZR Tactical Solutions, LLC - Home
I threaded the barrel on my saiga myself for a muzzle break. I found the job to be very easy. If you know what you need somebody may have one to lend. I was able to borrow the die I needed from another ingo member to do mine.
Heres a couple pictures of another Beretta 92 barrel I did today also, single point cut threads. I leave about .01" clearance between the suppressor and the slide. I hadn't wiped the threads off so there is a little dirt showing at the bottom of the threads.