For similar, if not matching, fabric, you might try Arlene Fowler of Fowler Interiors. She specializes in restoring/refurbishing Airstream/Argosy interiors. She restored the interior in my '64 Overlander and will be reworking the interior of my Argosy in the not too distant future. She has a tremendous selection of fabrics and may very well be able to find a close match for your original fabric. You can contact Fowler Interiors as follows:
Post Office Box 91
Symsonia, KY 42082
Welcome to the world of Vintage Airstreaming.
When you get ready, the furnace is not a difficult item to replace with a new modern unit.
Good luck with your Safari!