Just found it in my CTD catalog, and it looks like it's a DPMS Single Rail .750 Gas Block. Comes in .750 (PN: ARR-445) & .936 (PN: ARR-446) diameter, and it'll run you $30 + S&H. I'm sure you might be able to find it cheaper though, I just remember seeing it, and sure as hell it was in the catalog. Hope it helps out, good luck.
Last edited by XxChino13xX; 03-06-2012 at 02:25 PM.