Don't know how long it's going to last but I finally found the correct front parking brake cable for 1972 to 1978 pickups. Brand new, aftermarket, on Ebay, from several Thailand sellers. Quality in the pics looks good and they are only about $30 shipped to the U.S.
Just search "Toyota 46410-35051" on Ebay and you'll find them.

I know that the 46410-35151 cable IS available in the U.S. but it's intended for the 1979 to 1989 models. Don't try to make one of those work on a "78 or older model; it won't work. The ends & length are different.

Got one of the correct cables on order. When I get around to an install (could be a while) I'll post the results.