Here's a pic of a P99 with a factory threaded barrel. Problem is its REVERSE thread in metric. Go figure. Anyone know what can the factory had in mind when they made this piece?
I don't know if it will help but HK did the same thing with the SOCOM and tactical (socom = bassackwards tactical = normal)
Check out www.ccfa.com they make suppressors for different weapons. I haven't dealt with them but I have heard that they will do custom work. Over at HKPRO people seem to like his products. He also has something called a Neilson device that allows the purchase of one suppressor and with the device it is interchangable between the Tac and socom.