I've bought MKIII and 22/25 frames from drfrankenruger. The frames I believe come from builds where someone wanted VQ frames or bought a Lite just for the upper and this company sells the leftovers. Since MKIV platform is still new enough that there aren't any aftermarket frame options so there isn't a reason for there to be a surplus of frames. I'm sure once that changes, drfrankenruger will be the place to go.