Oddpb does it, but its pricy( any where from $300 - $650). Trey are one of the best though.
All in all there is a guy on the nation that i know that does some excellent laser engraving. If your interested in getting your gun one of a kind i would just get it engraved, plus its hella lot cheaper than getting a full anno. Also some annos have been knowing to screw up guns if you dont get it done from a quality place. You dont run that risk with laser engraving.
Check out oddpb's site though, as they is some amazing stuff on there even if you dont wan tot spend that much.