You can buy it in your hobby store.
Servo df-2000 20Kg metal gear
20 Kg actuating force, ball bearings and metal gears leave hardly anything to be desired!
The perfect power servo for RC car, flight and ship!
Actuating force: 20KG (6V) / 18KG (4,8V)
Actuating time: 0,15s (6V) / 0,17s (4,8V)
Metal gear + ball bearing