Another thought here is Lectric Limited (
https://www.lectriclimited.com
). I see the tilt switch available (apparently, these are currently manufactured in Taiwan), but again, on the chance that the Chevy or Olds crosses over for the non-tilt, they may have something for you.
There's also a switch rebuilding service the name of which escapes me at the moment. ISTR they boast of being able to rebuild almost any Delco Remy switch, going back to the early-early days.
More stuff to throw into the hopper.
A couple of years ago, the turn signal switch in my wife's daily driver ('97 Riviera) melted down. I ended up having to find a column (and the switch does not interchange as many years as the column - what a pain). The car was off the road for months while I tracked that down. Ugh. It's always the stupid stuff...