If your in Cali or Close Andy is the way to go. If your east coast keep an eye out. I am activly looking for a coach aroudn the same vintage (59-63) thats in rought shape to part out to get parts for our 59 I'm restoring. I have a person that I may take the remains and build a smaller coach out of. If I do this I will end up with a couple ribs.
That said you may have less problem then you think. I'm doing a full restore on a 59 and I have it appart to the point were the ribs are visable.
Airstream often cut ribs short and adjusted the lenght and spliced. About 1/2 the ribs in my coach are only half the width and end in the ceiling. This is because of window and door placement making it impossible for all ribs to be a full horseshoe. As long as you have the rib you could find some 6 inch peices and graft the rib back together by backing the splice up with the short peice of rib. That was standard practice at the factory. It's a sound repair.
If your missing the rib section then get the measurment of the missing span. Have Andy cut his ribs a little longer then you need to make them ship easy and buy one extra peice to cut splices out of.
I would be far more concerned about the cosmetic appearence from the outside then the ribs being cut. Factory there are no vertical seams between the caps. This aluminum the skin is made out of is not cheap but is available. I bought some from www.airpartsinc.com
and was pleased with the service and they were by far the cheapest price I found. Buy the "Coil" it's cheaper and you can get it in any length you need up too 100ft x 4ft.