Try Ecklers Trucks .
I just ordered the rear brake cable for my 56. I was cleaning the whole assembly and broke the screw end off one cable trying to remove a badly rusted nut. A little spendy, but they look right to me. BTW - welcome to Stovebolt! Have no idea why they have your post in Hi-Po unless you're going to hot rod it and that didn't sound like your question.

Dale