If you find one from an F150 (84 - up I think), it will have to be narrowed, but it will have a 31 spline diff and will be easy to mount your leaf spring pads at the right width.

The other option is a Ranger 8.8 rear, but those are pretty rare and thus expensive. A stock width ranger rear will fit, but here's the deal. You can buy an F150 housing, have it narrowed ($200 or less I think) and get axles from ANY ranger (they're all over Cophers). The axles you'll get are from a 7.5 rear, but they're the same as the 8.8. Although they won't be 31 spline, 28 spline should be fine for a truck.