Just be patient, they appear here every now and then. Also, keep an eye on e-bay. I've seen a few there. I got one for my '69 from a board member.
If you are going with big tires, I have heard the stock/dealer installed carriers don't hold more than a 33" tire. I'm not sure what causes the limitation though. There are a few guys on CK5.com that have either custom bumpers with spare tire carriers attached. Some are from
http://4x4iron.com