Jeff is on the money. Around here most of the paint stores will match a chip. If it's just a little touch up then you can probably pick up a little jar of matching touchup for less then $5.00. If you need more they'll mix you up a batch.
Take one of the units to an automotive parts store that sells automotive paint. (dupont for example) Most of them have a scanner and can match the paint and put it into a spray bomb for you. Reasonable cost to. John