Marcus, I misread your initial query. I think you are referring to the “boot” cover. Sunbeam Specialities has them custom-made with padding like originals. MKIA’s had the Pebble material. You should also get a new padded roll to properly install it.
Tonneau’s were also mentioned as a wish item. I’d be cautious with used ones. Even NOS or old good condition. They shrink and snaps generally do not line up. When buying new, make sure the snaps are not installed so you can put them where you need to. Most, if not all new tonneaus come with snaps separate.