You can go to a local automotive paint house or some auto parts stores, and they have a spectrophotometer. They use it to sample your current paint. Then they take the info from the photometer and mix up your color. They can put it in a pint can or even a spray bottle. My local O'reilly store did this for me. It cost around $40 for a pint, but it matched perfectly and I'll have plenty if I need to do it again.
