Forgive me if you know this already, but your Contemporary was built by a company owned by a guy named Peter Bayer. He sold Contemporary and went on to own Nisonger Instruments up in New York. Nisonger is the US distributor for Smiths gauges. If Nisonger doesn't sell the sending unit, they likey will know where to get one or how to substitute another. Hope this helps.
https://www.nisonger.com/