Bob,
one solution may be on these lines...................... https://www.hannants.co.uk/product/CA48050?result-token=7Lfdj
These are 48" which means that they will be 1" high = 25.4mm - in 1/144 that is the equivalent of 3.66m- a bit big - if you can get 24" Serial numbers in 1/48 ( 1.8m ), I reckon that may be fairly adjacent!
Modeldecal do the RAF Black serial numbers in many scales & sizes.
Sorry for jumping Imperial to metric, but I can only think in Metric!