I got one from M and M 4x4 in the UK for my 1984 ROW diesel. I dealt with Becci. It was not as outrageous as one might imagine. In fact, the rubber fuel filler hose was more than the tank. The tank was $71.40 (part #NRC9225). The fuel filler hose was $87.65 (NRC9291). If your setup is original, you'll probably need a new hose. You will also probably want to get a new sealing ring where the fuel guage mounts. There website is www.mm-4x4.com
Telephone is 44 (0) 1905-451-506. Good luck. By the way, you won't find these parts on their website as they are special order. I can't recall the exact shipping cost, but it wasn't astronomical.