Why do you want a mechanical one when you can easily make a reliable, fully electronic one for $5?
Excellent question! It's not for use in my car, it's for a mate who's designing a digital device to correct temp gauge readings in classic cars. He's onto the Mustang phase of his project and needs a regulator and temp gauges from various models to take measurements from. I'm supplying a gauge pod from a '71-'73 but don't have a spare regulator.
It needs to be original as the mechanical ones behave differently to the solid state versions.