I get my cork and paper gasket material at Tractor supply, in the tractor parts section. Comes in a roll, about a foot square when unrolled. I would not be surprised if auto parts places also have them.
Here's the stuff I used, can't recall if I bought on e-bay or not, probably.. NI Nickson Industries, Inc part no RK 1016 / 3157 it was 10" X 26" X 1/32" See image, says that it's best for sealing coolant, Gasoline and oil. It's described as a RUBBER - FIBER SHEET ... You want very good gas resilient material, once you get that gasket on and the tank mounted, you don't want to have any doubts.. When I rehabilitated my gas tank, i of course emptied the gas out, I filled it nearly to the top...with water hoped to purge all of the gas fumes then slowly removed the old rivets and used new ones.. Read up re safety when working on gas tanks etc etc P.S. I would avoid imitations and unknown manufacturers..and stick with U.S. MADE material from known reliable sources like Fel-Pro or NI....I would not look for the cheapest price, were talking gasoline here... etc etc ..WORK SAFE !! Only you can protect YOU..
I didn't see the NI product but the below search terms and Item number will get you to FEL-PRO Rubber-Fiber Sheet 36"x18"x1/32". For Sealing Water, Oil Or Gasoline... Rubber-Fiber Sheet 36"x18"x1/32". For Sealing Water, Oil Or Gasoline eBay Item number :133117063733
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