I went to my LBS for a road bike brake cable and was directed to the LBS "mechanic", who handed me a shift cable.
...Easy mistake to make.

"No, actually it's a road bike BRAKE cable I need"

So he handed me a mountain bike brake cable.

"No, you know, the kind with the bullet on the end, not the barrel"

- That seemed to do the trick, but I don't think I'll be going back there for a cotter.