Mac's makes them for their tuned pipes
http://www.macspro.com/accessories.asp
here is one
http://www3.towerhobbies.com/cgi-bin...&I=LXBWL5&P=ML
I think someone else makes them under their brand name too.
Of course with the nut on the inside of the muffler if it ever came loose, it would be doubtful that you'd lose it. So if it works go for it.