If my memory is correct, the switch should be in the treadle valve just above the brake pedal. There may be 2 switches, one for brake lights, another for the air pressure buzzer.
Try Eastside Ag in Yorkton they are the Agco dealer but they have two or three Deere's on their lot and they are looking to move them give them a call ask for Frank 306-783-2442. Good luck