Here are some links to places that are great for modelling and prosthetic supplies, just click the links below.
Nimba Creations Fabulous for Prosthetics and Gore stuff.
Tiranti Leading UK manufacturer and supplier of Sculptors' Tools, Materials and Studio Equipment, for Carving, Modelling, Mouldmaking, Casting & Restoration. Dedicated to supplying sculptors worldwide since 1895.
4DModelShop Model Making Materials Fabulous for all sorts of model making materials.