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...