[spectrrr]

If you want to build it from the ground up, Midway has a stripped flat top upper for $109, be about $126 after you add in the forward assist and ejection port cover (all in stock)

If you want to go the SBR route, I have a Daniel Defense 12.5" barrel which they mistakenly sent me, I'm sending it back tomorrow, but you're welcome to it for whatever I paid (I think $279) -- you'll still need a barrel nut, gas block/tube, and hand guard.

Charging handles are still readily available, $20-$45

The bolt carrier group is a B!TCH to find right now. Single hardest part to locate, more so than lowers.

Otherwise, I've seen Palmetto sporadically getting in a few 16" uppers for sale in the last few days. But over course, You're looking it probably a 4-5 weeks shipping delay from them. I ordered a 16" upper minus BCG from them on 12/31 and am still waiting for shipment. (they're good people, they'll ship, just taking a while)