From the cross-reference at Partzilla a number of 70s models had the same RH handlebar control & lighting switch knob.
Not $15 cheap, but using the x-ref there's a complete 750B RH handlebar control on EB for $25T+tax
with Make Offer button, so you can probably get it for a bit less than that.
I scanned fleabay start switches but getting a buyer to look inside a to answer a question is unlikely to happen. I put the switch back together with the head light left in the on position. If anyone runs across this part I'm happy to buy it......