Gemtech makes one for the Barrett. I've seen it on display at the Shot Show. Gemtech makes excellent equipment. Their "Hushpuppy" system (basically a drop in barrell for the 10-22) is amazing. All you hear when shooting it is the action moving.
The oasis product are excellent, I have a mark II pistol setup by Jim Pixley with the front sight set back so the barrel can be threaded. All the slide and springs all worked on to make it very quiet.
http://www.gem-tech.com/OASIS.htmlThink its SWR makes suppressor for the barrett