try a narrow boat chandlery for boat blacking or google for intertuff boat blacking,its usualy sold in 5 liter tins upwards but you wont want anything bigger,i can get 4 coats on a 60 foot boat out of 20 liters,but it may not be as cheap as machine marts shutz,used to be able to get bitumastic from countrywise stores but they have stoped doing it i think it was called buttoline bitumastic.