if you have a nfa tax stamp for your ar15 you can get in touch with cmmg or ceiner. ceiner makes fa kits to run 22lr through a properly registered ar15/m16. personally i would wait till cmmg finishes theirs. no matter who go to you, yu will have to present proper paperwork that your firearm is a legally registered and stamped nfa item.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent