Other years, I have used Michael Moore's "Bowling for Columbine" when working on gun control. This year, however, I have not found the time to do so. I have nevertheless shown this presentation of American history taken from the film.
Under is a list of more articles on this topic. Some of these articles are a bit old, but they can still work as a point of departure in discussions and for giving more information.
You should also visit my colleague Anne's blog to see her lesson plan on gun control.