With the banning, confiscation, and destruction of firearms, Hollywood suffers incredible losses at the box office since firearms are unable to be used as props and action movies and television shows are therefore no longer produced.
I realize that you're probably joking, but the reality is that many existing gun control laws make exceptions for theatrical performances. That's how you see full auto weapons produced after 1986 in movies. Alternatively, they can always go to another nation where firearms are available for such purposes (i.e. P90s might not be allowed in CA but they can in Canada where Stargate was filmed).