The parking brake cables finally arrived today... they were special order Genuine BMW parts, at like $54 each. A bit pricey, but I wanted working parking brake cables and didn't feel like waiting for a 318ti to come up in the yards.
Removing the existing parking brake cables and putting them next to the new ones, it was clear that the old cables were far too short. Here's the comparison between E36 parking brake cables and 318ti parking brake cables:
Installing them went pretty easily, the joys of working on rust-free southwest cars!
After adjusting the parking brakes at each wheel and then at the handle, I was rewarded with a tight, immensely satisfying parking brake that locks the rear wheels in 3 clicks. I love it when a plan comes together.
I know it's silly to get so excited about a working parking brake, but I have pretty high standards for all my cars and require every single thing to work before I do any fun/performance mods.