Most decent chandlerys will sell clear gelcoat, catalyst and the coloured pigments for the job, a good tip once you have applied the gel coat is use sticky tape over it, this keeps the air away and makes it more shiney like new gel, or you could add a tiny amount of mould release wax to the mix.
ROAD USER has jellcoat filler in tubes,(I also think HALFORDS do too) white with hardner and a small spatula. Is great staff. For colour just get paint (same as that that you paint fridges don't know what the type is in English) and mix it with it. It will do the trick.Good luck
