Mark,
BRM has only produced 3 gear sizes for angle-winders (38, 41 and 42); you can find them at 132slotcar.us. I do not recommend using non-BRM gears – the motor position cannot be adjusted in the chassis and it requires variable pitch gears.
Regarding the angle-winder conversion: I have not bought a kit but these articles cover the conversion:
https://slotcarillustrated.com/portal/forums/showthread.php?t=80731
https://www.slotcarillustrated.com/portal/forums/showthread.php?t=79021