If you can't find a match among the available nail polishes and car touch-up paints, go to a hobby shop and pick up some model enamel.
I bought a used pick-up truck when I was in high school and it had several on the sides and tailgate. I couldn't find any automotive paint that matched the light blue color so I bought a bottle of blue Testors brand model paint along with a bottle of white and a bottle of thinner. I poured out the thinner and mixed blue and white in the empty thinner bottle until I achieved a really close match. If you need a metallic paint, then buy a color that is too dark and use silver or silver and white to lighten it.