Depends on why you want it. If you're just wanting to pad the ol' resume, Chris Rock is right -- don't bother. It's not "important" in that sense -- unlike law school, you're not really expected to have relevant jobs every summer.
For me, though, I wanted to find out as soon as possible if a legal career was really for me. Obviously being a lawyer isn't like watching a courtroom show... I wanted to see what it was really like. I wanted to do that as soon as possible because I intended to get a liberal arts degree, which is a great education but not terribly practical. So if I decided law school was out, I wanted to have as much time as possible to re-focus my studies and possibly change my major to something that would prepare me for a career or at least (non-law) grad school. So in that sense, yes, it might be helpful to get one now.
Plus, I really enjoyed my internship. To me, it was more interesting and better-paying than working at the pool or Taco Bell or whatever. But everyone's different.
As for finding one, try to find a family or friend connection that will let you work for them. Even small firms need runners and stuff like that.