Unknown manufacturer, but it resembles a JP Enterprises item. It might be a Midwest Industries. Like new, just two minor scuff marks. $25.00 shipped in CONUS. Sorry, but I don't know anything about this block other than what it looks like or what make it might be. Steel? Not sure. Looks like the gas block mounts from the bottom with two set screws (or pins).
Lowballers: If you don't like the prices MOVE ON!
H&K, PTR-91 Brake: $30.00
MagPul (Originals) 1-OD, 1-Black: $3.00 ea. MagPuls SOLD
Tango Down Battlegrip: $20.00
Please PM me if interested. Pics on request.