Fuel tank sending units for dealer aux. tanks on truck

[Jerblazer72]

Guys,
I just bought a set of "dealer option" auxilliary tanks for my 72 gmc. They did not have a fuel gauge on them, just the sending unit. The PO of my truck removed the tanks from the truck I now own. It was set up with a switch to change the fuel gauge from each tank so that you know what you have in each. I would like to put sending units with fuel gauges back into the tanks that I just purchsed. Do any of the venders here on the site sell the sending units that I would need? If not, does anyone have a recommendation of where I can purchase two of them? Also, do they need to be 90 ohm? (from what I have read, I think they do)
Thanks for your help.