Airsoft parts has V3 AK gearboxes that should fit the G36. May I suggest the LCT V3 gearbox as being a pretty good one. He also stocks the KA V3 gearbox as well. Only thing you'll need to change is the selector plate but you can take that off your current broken gearbox or buy one for like $10 or whatever.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE