I Googled how to measure the size of the wheel, # of lug nuts, distance between the lugs etc. and went to my local junk yard with the numbers. I told the guy I wanted a Ford 450 rim and it took him 10 minutes to find one for $75. I tried it on to be sure it was correct, sanded it a little and painted it so it looks like new and hopefully will never touch the ground. There is a "Spare Tire" post with a lot of good info on this subject if you want to search around for a while.
Here is a link that gives some info on measuring the rim needed including the bolt pattern.
This link discusses the "winch" from Teca that I and others used to lift a spare up into the available space under our rigs. I think it works very well even though I've only made it go up and down 4-5 times, but it has also held the spare very securely for thousands of miles. I am very happy I added this to my GreyHawk.