SayUncle reported that Bison Armory are selling new 6.8 SPC AR-15 upper recievers. From BisonArmory.com:

We just got our 18″ and 20″ 6.8 SPC barrels today! I’ve put together the first upper for testing. It’s a 20″ with unthreaded muzzle. Pictured below is the upper with a Young Mfg. Match bolt carrier, YHM lightweight four-rail rifle length hand guard, and YHM A3 flat top upper receiver. The upper also features an intermediate-length gas system, YHM low profile gas block, and YHM forearm end cap.

These photos of the uppers were posted on 68forums.com:

The first upper is the most basic, 20″ with threaded muzzle, Phantom .308 FH, Bushnell 3-15×50 scope and rifle length gas system. The second one is the 20″ unthreaded with intermediate-length gas system.

The first upper in this photo is an 18″ with a Saylors Machine Phoenix FH and mid length gas system. The bottom one is an 18″ with a TNW gas piston system and DPMS Levang linear compensator. I’m really looking forward to trying out the GP system.