Are you sure they were in the original scenery from Lawrie? e.g. do you have screenshots showing them in the sim? If so then yep would be a missing library maybe, but if not they may never have been in his AFCAD to begin with.
You should take a look at ADE and try adding them in yourself using default FS9 buildings, it's not too hard after you've followed some tutorials.
see:
https://www.scruffyducksoftware.com/air ... ign-editor