An international airport/airbase on the north coast just east of Paleto Bay.

For the Concordes to spawn, download this:
https://www.gta5-mods.com/vehicles/concorde

Installation:

1: Install this mod:
https://www.gta5-mods.com/scripts/menyoo-pc-sp

2: Extract "North East Paleto Bay Intl.xml" to "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\menyooStuff\Spooner"