Could you get the material at a fabric shop and have an upholsterer make you a set?
There is likely a more durable material available today, IIRC those were vinyl and didn't do well in the cold (or at least that's what I've heard).
If not there then a marine upholstery shop or a tarp maker (like the ones for the soft sided cargo trailers on the highway) should have something.
As for a direct fit set, the street rod or lead sled crowd might have something, but I don't know where to point you on that.
