That particular fuel tank might be the same one which that platform started life with back in 1974, I suspect. Might have to search some of the parts suppliers' websites for fuel tanks and then possibly a link for a sending unit repair station or similar. Might also be some NOS ones in nooks and crannies at dealerships somewhere too, but that's somewhat doubtful at this time. If you can get a good part number from the dealer, you can use
www.partsvoice.com to do dealership searches. Maybe your local dealership also has a "Dealer-to-Dealer" (or "D2D") link that would do the same thing?