Lots of info on how to do them yourself. Brownells sells a pretty simple jig, and has a decent write-up on the process. If you're careful it's doable without the jig toI, I've done a few freehand. You also need to make sure the trigger slides freely in the trigger bar tracks, and probably tweak the sear spring a bit. Check your angles for sear engagement often and don't use power tools.
Kristian