the issue you will have is what paint bites onto the vinyl. most don’t and will flake/chip off. frog-juice do a paint in aerosol form that you can apply colour blends etc but obviously not for an airbrush gun.
before we bought our printer i would often use ink in an spray gun for large banners even curtain sided trucks. a hand held aerosol can with "ink" in it for vinyl or even a small 4 inch roller, or as i said, frog-juice aerosol.
for colour matching i would mix an ink myself then go into a auto paint supply company in our industrial estate and they would install the ink in the spray can. it is so much cheaper doing this than buying cans because you would not beleive just how little paint is in an aerosol.
the ink i used was from either sericol or for a better priced ink you should use Appollo Inks.