Fulton Armory has some for their Titan .308 (DPMS compatible) rifles in both black/phosphate and chromed according to their webiste but their comms are non-existent and there have been reports of things supposedly in stock when ordered that were NOT in stock in reality. If you order from them, you may get it and you may not, but they aren't taking backorders so you really aren't out anything.
If you need it RIGHT NOW and Fulton doesn't help you...your options are limited to: a) GunBroker and GunBroker prices; or 2) BARFCOM's AR-10 EE Subforum (and BARFCOM prices).
BCGs are still one of the most difficult-to-source parts because many mfgs are holding their stock for full builds rather than parting with precious inventory for individual sales of parts. Keep on your backorder, get on the wait list at places like MidwayUSA, Rainier Arms, DSG Arms, 762SASS, etc., etc., and be patient or go for the above now and be spendy.