As all parts for these cars, they are far and few between. They occasionally appear on Ebay. There was one two weeks ago. Be ready to pay some $$$$$$. Bought mine a few years back and I paid a premium then.
There are all kinds of restoration sites to choose from. The only one I can think of is CJ Pony Parts at the moment. Also, your local auto-parts stores maybe. Junkyard is also worth a shot
The fuel sender is in the fuel tank and is what your fuel line hooks to the sender has your fuel line that supplies fuel to the fuel pump and it has a sending unit that sends a signal to your fuel gauge in the dash