Where to find video footage of Kennedy's and other Presidents?

I need a some presidential videos, because for Father's Day I am editing together a film of certain footage that my Dad was captured in. He was an officer in Washington D.C. for decades and worked for the Kennedy's, Nixon, Clinton and others. He can be seen in both the Kennedy's funerals and in Nixon's helicopter (I think) take off quite plainly. I know of a couple doentaries that have this footage in them (History Channel's Vietnam 10,000 Days and others). My question is where can I find these doentaries and does anyone know of other places to find this footage? Thanks!