Thats gonna be a tough one.
I don't think scrapyards would keep anything that old and worth money to someone.
There are guys that will answer you back that may have leads for you.
They are out there but someone owns it so it'll be a barter or buy deal.
Try the appropriate motor forums and off course the correct year forum for your truck.
There are trucks that come up for sale that you can use as parts donors. Again though it'll take some digging.
I run up and down the state a bit so I'll keep it in the back of my very shallow mind.
Good hunting.