What’s the boat ? If a mainstream brand such as Fairline, Princess or Sunseeker, then they have all used their own versions of the same gelcoats for 20+ years. In which case find out which it is and buy some. Lesser brands will have shopped about on price each year and so then you’ll need a mixologist to sort you out but with the lesser brands more prone to fading over time, it wont be easy i’d say, but it is doable.