ive had aliexpress suggesting i buy gauges which honestly are tempting. but they dont really fit in with the original aestetic.
i would expect it to be fairly straighforward to pick one of those, and print the backing to match and just swap the backing. the final step may be (if your not lucky) to add a voltage control unit to reinterpret the voltage from the car to something that reads correctly in the aliexpress dials (note, such gadget would also be used to get the temp gauge right).
its one of those things where, "if one of the more 'hands on' members absolutely needed it, and the part was ridiculously expensive/impossible to get, and he could be bothered to describe the process" (AKA the planets align) it would be really easy to copy their findings.
unfortunately for you.. i know what i would do, but i have no need for doing it.
however, we as a group will be very supportive of your attempt and im sure a handfull will be chipping in advice if you start the project and report on the progress.