I got LUCKY! I found a almost complete 1977 F150 in a local wrecking yard in rural Eastern Arizona last summer. I think the truck had been in someones yard or barn for years before it was sold to the wrecking yard. It was at the front end of a row of various Fords and apparently had just arrived at the wrecking yard when I found it. Axle was in decent shape with 4:09 gears and the 1/2" thick axle tubes, which all 76's had and only some 77's had.
I paid $250 for it and they gave it to me complete, with the radius arms, springs, white spoke wheels and rotted tires. Sold the radius arm set for $150. and the gears for $50, still trying to sell the axles, then used the housing to shorten to add a HP 44 to my Bronco.
I've also seen a few 76/77 housings or complete axles show up on Craig's List and Ebay but they are usually listed at $500 or higher. Good luck in your search, they are out there still. Of course, for a PRICE, Currie can build a new HP 44 Bronco width axle for you with the heavier duty Dana 60 style Pinon.