Archon Type B magazine release kit. Factory OEM.
In the kit:
1× Magazine Catch Spring (Pos. 37)
1× Magazine Catch (Pos. 36)
1× Magazine Catch Button (Pos. 38)
1× Magazine Plate Button (Pos. 39)
1× Magazine Catch Screw (Pos. 40)
1× Magazine Catch Pin (Pos. 41)
Confirm it fits your Type B. Installation and final safety checks belong to a qualified gunsmith when that is the right call.