Well, I think you'll be hard pressed to find those without buying new cans or a crashed set and swapping them...that said, this dude
http://www.carbonpartz.net/id94.html sells mufflers and parts(including conical end caps) so if the sleeve is a common size that he happens to sell then you're probably in luck. I've got no FHE with his parts but so far communication has been A+.