What GM cars in or around 1965 came with rear disc brakes?

In 1965, GM's use of rear disc brakes was extremely limited, and almost exclusively found as an option on high-performance models. There weren't any standard models offering them. Even then, it wasn't a widespread option.

Your best bet to find a 1965 GM car with rear disc brakes would be to look at some of the higher-performance models, though confirmation would require checking the specific vehicle's build sheet. Even then, it's unlikely you'd find many. The technology was still quite new and expensive.