Lightning is just not for supercell thunderstorms. They can accompany volcanic eruptions as well.
Take a look at this video of lightning in a volcano's eruption cloud, as lava enters the ocean in the Kalapana area of Hawaii in 2008, courtesy of Ranjit Mathoda:
Ask anyone who witnessed the eruption of Mt. St. Helens in 1980 and they can also vouch for the phonemenon as there were frequent lightning strikes.