there's a very easy way to do it (even though everyone has probably unlocked them/already knows about it)

don't read on if you'd rather work your way through.











once the credits you've spent and the credits you have left total about 9 - 10 million, downgrade all your ships, then go and upgrade one of them as much as you can to unlock the lead pilot from that team. once you've confirmed the upgrade and unlocked the lead pilot for that team, downgrade the ship you just upgraded, go to another team and unlock the lead pilot on that one. the first lead pilot wil stay unlocked, so you can go through all your teams and unlock every pilot.

(apologies if everyone already knew this).