Any mower key switch would be fine
However which one depends upon what else goes through the switch, things like starter , lights, electric PTO, recharging wire , boom sprayer etc etc etc .
Here are a few options
https://www.stens.com/search?keywords=ignition switch .
Car switches will not work on magneto engines because you need to short out the magneto to turn them off
So any switch with 4 or more positions would work.