The, now civilian, ex-military flying unit at which I work still has a box of brand new ones in the stationery cupboard. I don't think anybody's used one in years.
I remember as a Cadet Pilot on the mighty Bulldog that you used to lean to a 6.5psi fuel pressure as we climbed through 1500ft, and dutifully put a chinagraph mark next to the lever in exactly the same place as the last several hundred students, so that you knew where to return the mixture control to after any manoeuvering at altitude.
G