Modelling doesn't really require any equipment at all. You'll be able to get by perfectly well with a rolling pin, some kind of pointy stick and a sharp knife.

If you feel the need for more gadgets you'll find all sorts of tools and cutters down at your local craft store (or toy store - check out the playdoh section!). If you have a professional cookware shop near you they'll have a range molds and tools available to help as well. Roller cutters are useful, they're available now with interchangable wheels so you can cut patterned edges (try the toy store, or the pastry section in the cookware shop). A pizza cutter makes a fair substitute so long as you don't want to do any detail work.