I've got a couple of hundred of these...
Easy to obtain, just go to a wrecking yard and carry a brass hammer with you. Or be prepared to screw a lug nut on so you don't damage the thread when you belt them out, to do this you need to screw it on at least five or six turns, but not so much that the stud comes out the back end.
You will find the right studs on pickup and van rear ends right into the eighties, probably nineties. From about '74 on they have right hand threads both sides, which makes it easier.
Later rear ends have longer studs too, maybe a quarter inch longer, but they fit just the same.
Ray