I'm gonna take a guess you're limited to a donor truck unfortunately. I have seen windshields for 2nd gen Hilux (72-78) but not for the 1st gen. You could try calling up a glass company, perhaps they have more knowledge from being in the business than the internet tells us in quick searches
I'm afraid you're guess is right seems like maybe I've tracked down a door glass but no luck on the windshield I've already made a few call and checked a few local places with no success. I was hoping someone here knew of a custom place or anything to help mine is still there just has has a small crack so will eventually need one