If you source the BCG from Brownells it’s cheaper to build one, unless you want junk. I can’t link where you buy the junk lol. I also got the magwell adapter I use from Stern, drops out like a mag for quick swaps on uppers/calibers (has another button to drop the 9mm mags). Ballistic Advantage has good 9mm AR barrels, not really experienced with others available.
Edit: I didn’t think of IRG, but they do have some offerings that are not junk.