woof359,
As pointed out, there are some work-arounds that will get your parking brake to function. I'm not sure how deep your pockets are so maybe using a work-around solution is the way to go. What's the condition of the entire brake system? I think you mentioned a new master cylinder. How are the wheel cylinders and brake lines and hoses? Whatever you do, do not try to save a few bucks on brakes.
Here's another option to consider:
Bowtie Bits Antique Truck Parts. It appears these are steel wrapped cables.
Keep us posted, we're here to help.
Good luck,
