Most paint stores that carry automotive paint should be able to mix some for you. The only drawback being the pint that you would have to buy. It would also be helpful to know what type of paint that you now have ie enamel polyeurethane ect.
California Mustang has it in 12oz. aerosol spray cans for less than the previous post. If you just need to paint over a scratch and don't want to spray the car, than spray some in a small jar and then use a small brush.