It's a six hole CAR handguard. It could be Colt or Diemaco. Most aftermarket are seven hole and not as sturdy.
They're getting hard to find and as such can fetch a premium with the retro crowd. I'm always keeping my eyes open for them.
Of course while I'm typing this I'm sure a few have offered to take them off your hands. Not terrible valuable but they look pretty new so I'd say $30-40. Less if they prove to be aftermarket.