Where to get Parking Brake Release Handle and Cable?

I need to replace the "Parking Release" handle and its short cable that runs from under the dash to the parking brake. Mine is broken in two different ways.

For an '83 Riviera, my parts book shows group 4.594 and part 1261708.

But, I can't find that part number anywhere online, and local stores don't have generic replacements.

Any suggestions? I'm surprised that this part is not easily available.

Yes, I do have a parts car; but that part, while it looks OK, is the same age, and I hesitate to disable part of the brake system on a car that has to be pushed around.