Here maybe? Well, it's the official trailer at least, but it doesn't feature much music. Much more hits for Lord of the Flies on YouTube if you search for it using that title... Unfortunately, many fragments don't seem to use original sound and music, but there might be something.
I used to have this film on VHS when I taught senior English to unsuspecting teenagers. I probably left it in the English department video library. (I never had much success with that book in the classroom) You might find it at your local video rental... but get the 1963 black and white version, not the horrendous remake) In the original film, director Peter Brook used a paperback copy of the novel as a shooting script, and interspersed "reality" footage of the kids interacting. The film seems artless, but is quite effective.
Tom, on Point Pelee, Canada
Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...