Try something like this:
https://www.homedepot.com/p/CRC-QD-1...30-6/202262505
If you're good with your hands, you can disassemble switch and lightly sand corrosion off contact areas. Be careful of little spring size of grain of rice.
Otherwise look in junkyards or call around. You can also use left-hand controls from another bike. Looks identical to stuff off '90s CBR600s.