Joe Bob's has 'em:
$154.95, free shipping orders over $90.
JoeBobOutfitters Premium Complete M16/AR15 BCG with MPI Testing
These BCG's are fully assembled and ready to drop in any AR15 or M16 rifle or pistol. These are the heavier M16 carrier and will work with any AR15 platform rifle designed to use a standard BCG. Calibers this BCG will work with include 5.56, 223, 204,and 300BLK.
Mil-Spec MIL-STD-171 Phosphate Finish
Individually MPI Tested & Engraved.
Bolt: 9310-Case hardened, Shot Peened, and MPI tested.
Carrier: 8620 Tool Steel-(M16 full shroud)-Heat Treated, Case Hardened, & Chrome Lined.
Gas Key: Chrome Lined-Grade 8 Hardened Fasteners, Permatex No. 3 sealed, Torqued to 60 in lbs, & Mil-Spec Staked
Cam Pin: 4340 Steel-Heat Treated & Phosphated
Extractor:Tool steel S7-Heat Treated to 48-53 Rockwell C & Phosphated
Extractor Spring:Upgraded Chrome Silicon. Black Buffer & O-Ring* for Enhanced Reliability.
*O-ring is not installed, but is included in packaging