If your fridge is an original '69...most likely your best chance at finding replacement racks is with a RV boneyard. And even then, the shelves are not likely to be in much better condition than your own. The good news is, the fridges aren't Airstream specific so there ar elots out there. I found some missing parts for my '64 at Cherokee RV in Denver, although they are not currently in business - in-between moves (or something). There are similar places across th country.
Your best bet would be to clean yours up, even if it means soda blasting - then either re-chrome or paint them with epoxy paint. I plan on doing that with my '56 which is currently undergoing restoration.