When I was in teaching, our Science Department staff got fed up with colleagues constantly using up their supplies of acetone. Why? Because it's great for removing chewing gum!
So where (apart from school science labs) can you get acetone? No problem. Just buy a bottle of cheap nail varnish remover. (Check the label, though. Some products now declare that they're 'acetone-free'. You want the old-fashioned type. If you buy it from a chemist's shop, the pharmacist will be able to confirm that you've got the right product).
Chris