I’m always surprised that requests for vintage items like this are seldom met with “they’re rarer than hen’s teeth”.

I take it from your post that you have already tried to find one of these gauges ?, & therefore know if they are rare or not.
If everyone posted the “rarer than hens teeth” comment, then threads like the Hornet project, Whitley project, Stirling project & Wyvern project etc would be full of little else.

I most certainly wouldn’t put these gauges in the hens teeth category, given that I saw several of them for sale on evilbay last year.

Bob T.