I found something close to it. If you're talking about that waffle pattern like that's in the truck lid (like on my 1940 Deluxe). There's a vintage Pontiac vendor here in SoCal that carries the material. It's pricey for how much you get, and the pattern is smaller than the original for a Ford, but it's close enough for me considering it's discontinued everywhere.
Link:
https://www.pontiacparts.net/product...24-x-36-sheet/
The original is basically thick roofing paper stamped with the pattern. If you can stamp the pattern yourself, you can buy a huge roll of it at Home Depot for much cheaper.