Check with BroncoHut Marsh. I've heard Melissa came up with some stock of similar at least, if not exact duplicates of the original.
There were a couple of different ones over the years and models too, if I remember, so if you're looking to replace some existing stuff exactly, find out it you're looking for "hounds tooth" vs "herring bone" or some variation on those themes.
You can sometimes get lucky with upholstery suppliers too. A local friend found some exact repro material for his '74 Ranger a few years ago, but it was supposedly the very last stuff that the vendor had.
Good luck.
Paul