https://www.joeboboutfitters.com/Kaw-Valley-Precision-8-5-9MM-4150-QPQ-AR-15-Barre-p/kvp-9mm-bbl-8.htm
https://davidsondefense.com/Gauntlet-Arms-Facha-AR-15-8-9MM-Barrel-110T-Phosphate-Finish_p_5135.html
I’m not recommending these since I have no history with them. Lots out there in the world
i had a pof lower with a RRA upper. POF sold a little sleeve for front pin that tightened it up. i searched my emails but cannot find where i bought it.
check this thread - post number 2 - https://forum.308ar.com/topic/321-pofdpms-build/