Apologies. No internet for the last 3 months. (!)
Factory material is impossible to find.
GM holds proprietary rights on all their fabrics. There has never been any comparable produced by the secondary market. Only source has always been directly from GM. For stupid $$$. A similar performing material (in construction, not pattern/design) produced aftermarket sells for $30-$40/yd. (36"x54"). That factory GM stuff, even when you could get it way back when, would be priced at (*cough*) $130-$150/yd. Yea.
Only way you might ever find any would be if some partsman came across a long-forgotten roll in the back of a warehouse.
Good luck on that.
Measure out how much for each panel. I think that the side panels of bucket's backrest side panels may have enough fabric that you could cut them out of some seats at the junkyard.
I've stitched smaller pieces together to get large enough pieces. Fabric from various seat 400 panels. Rear seats are the best to get that. Lower usage.
The seam ran parallel to the top edge, about 1/3rd down and followed the front curve at the same distance to wrap over at the bottom edge. Kinda hockey-stick shaped.
Nice simple decorative single top-stitch.