Chris, House of Resin in Wareham has everything you need for resin casting. However, it seems most turners use Glasscast 50 for wood. Glasscast comes in 3 sizes: 3, 10 and 50 which relate to the depth you can cast in one go. Stiles & Bates in Dover are recokoned to be the best source for Glasscast. There's also Eli-Chem Resin over near Godalming but I think they have mainly #3.
Hope this helps.