Where to buy a new Fuel Sending unit.

The main problem I have with the new senders is that they read linear, the original senders where non linear. If you look at the fuel tank, you will see because of the spare tire inset in the tank , when the fuel level is halfway down the tank, you have actually more than half of the fuel left. Have not been able to find a non linear sender. Some one here could make a mint supplying just the non linear wiper assy.