Hi,
I've heard it referred to as a "swing-off" mount. This was factory installed by Steyr back in the 50s when the rifle was built. I haven't looked for one myself, but would start my search with New England Custom guns. There is probably one made in Germany by EAW, etc that they're importing. I'm guessing cost would be comparable to, maybe a little less than claw mounts. This is a super secure set up; the Mannlicher's split rear bridge required outside the box solutions so no need to get this fancy for a standard double bridge, etc bolt rifle.
Bill
