Some objects can be "borrowed" from current scenery, but it isn't a straight-forward conversion.
You can get a large number of airport objects from the World Scenery pack.
I downloaded only the Objects folder to correct missing objects and textures at another airport.
https://github.com/FGMEMBERS-TERRAGIT/terraGITFrom my rather limited experience, most terminal buildings are modular, constructed of a bunch of different objects.
Normally a building (one object) with gates (other objects) attached. You have to move all of them sometimes to get it to look right.