So far only Jarvis makes an extended/threaded barrel for the Five Seven pistol, and they only make a new batch every few months, so they are scarce at times.
There is a company that makes 5.7x28 barrels for the TC contender, and that could be turned down and threaded for a suppressed project gun
2008 will bring more suppressor friendly choices in 5.7 firearms.
Lighten up Francis!.....;Actor Warren Oats, in the movie "Stripes"