Than you very much for your answer.
I have a video clip where the reaction is shown. You you can find it at http://faraday.physics.uiowa.edu/chem/10A10.50.htm (labeled as "MPEG Movie (8.62 MB)"

In Spain (my country) is possible to find the potassium permanganate at chemical products store. I'd try to find it at the pharmacies but, although they ususally work with this component, they are not authorized to deal it.