Potassium permanganate is sometimes sold in fish (aquarium) stores as a tank disinfectant over here.
New rules apply to chemical sales after Sept 11 so I am not sure if this is easy to get or not now. As a chemist I just got it from the lab. Fun stuff for fire, not a very good water disinfectant, stains everything purple/brown, and can severely damage mucus membranes or your eyes if the powder gets in them. Be very careful with the pure powder.