I'll add a a little to the above info from my findings:
That switch was actually a parking brake indicator switch in some of the GM cars. It was made by Indak, Ive nver seen a direct fit one but they could be modded on the bracket to work like the fox bracket. but they are not easy to find either. Not all cars were factory fitted with the brake indicator, don't usually see them listed on their own only with Accessory kits where the bracket is usually different (and pretty pricey).
the switch can be found with a lot of different variations on the bracket part, and you can take it apart and somewhat "service" it and get them working again if you are lucky enough to still find early cars in a junkyard near you to pull one from (all them around here were crushed when scrap went up).
this one is listed as a 1963 impala and is about the closest to the actual fox style bracket I was ever able to find: