What are physical therapy exercises for game keeper's thumb?

Not much. Unfortunately there is not a lot of therapy for a gamekeeper or skiers thumb. If it is not severe then a period of splinting for 3 to 6 weeks can be used followed by motion exercises. If it is severe, and an orthopedist must determine that, then surgery s treatment of choice.
Let me explain. If you have complete ligament rupture surgery is better method for treatment. If you partial tear or have surgery pt is very good method to regain strength. Splinting to support or rest affected area. Therapeutic exercises including stretching and strengthening exercises to regain range of motion and strengthen the hand and effected area. Modalities, ultrasound, electrical stimulation ice.