Hello Pykie,
I hang zillions of doors, sometimes surveying finished openings hundreds of miles from my shop, then pre-sizing, hinging, and installing locksets, etc. back at my shop before heading back to install all en masse. Door work was in fact what inspired me to invent the How Far Out gauge.
I have one company, Glass Haus AU, in Australia that might be able to supply you with gauges right now. Keep in mind that the only model currently available is Imperial scale only. If that will work for you, please contact Jordan Harman at glasshouseau@gmail.com. Jordan was one of the first to approach me about international distributorship. When the combo inch/metric ship after the first of the year, he will have those available as well.
Thanks for your interest.
Mike