If you have no luck here, I'm pretty sure it's the same connector used in a variety of places around the car (like fog lights), across multiple models. I'd unscrew the switch, take it to a junkyard with a few Volvos and start looking, you should find it in a few minutes.
Thanks for the tip on that. I was looking around my engine bay and I have an unused connector from the kickdown solenoid that used to attach to the automatic throttle cable. I switched to manual trans and put in a manual throttle cable, so that plug is unused now. I am going to check and see if that plug will in fact fit the reverse light switch, and I might be in business!