where to get paint matchup?

i had quite a dents and scrathes on m 02 TL-S I am thinking to do a touch up paint. For the job, I'd rather do myself since it is just a touch up. I am wondering where to get paints mixed up? I heard in the past from someone that once it is decades old the color code matching at dealer does ont work because of the aging effect on the body color. :thumbsup:
Thanks.,