Unfortunately, I don't think you will be able to match it that way. Even if you can locate the exact color, it is unlikely it will match the boat due to the gelcoat fading over time. We had some repairs done on a sailboat a few years ago, and the guy who did the work had to mix four different colors to match various parts of the hull. He used a device that determines the correct mixture, sort of like what they do for paint when you bring in a sample. In lieu of the professional equipment, you will need to mix it up to get the best match. Here are links to some good videos that explain the process (parts 1 & 2):
Basics On Gelcoat Color Matching : Boatworks Today
Gelcoat Color Matching (Part 2) : Boatworks Today