Oh, where to start...
Thanks for doing this Karen. BTW I'm the "Carl".
This post will 100% guaranteed get me kicked of the forum and maybe the planet too but 1/72 is a good scale ...
Anything 1940-50-60s RCN/RCAF. For example something similar this OOP helo sheet. Do not need exact A/C serials but the pieces to build one up.
Or two+three or three+three Air Force serial numbers. For example 101xxx was used by Voodoos, 104xxx by Starfighters, 107xxx by the Argus etc.
So how about unused ranges like 90-99xxx, 100xxx, 102xxx, 103xxx, 105xxx, 106xxx, 108xxx and so on. Xtradecal already did this using 109xxx for the TSR2.
You cannot have enough RCAF/CAF Lightning bolts. If you need some data/images, I have quite a few books on this subject.
And finally maybe something space related. IE USAF "Space Command" or RAF "Space Force" decals for the RAE. OR.9001 “SPACE FIGHTER”.