For starters google X-Ray Dog.find that that way.

Also do you want film scores or music from trailers? Trailers have often used scores from other movies just for the trailer. Depending when the movie is finished and trailers cut sometimes they will use actual pieces for the movies finished score it they are done.
During rough cuts of movies temp track from other soundtracks have been used till the real score is done.

Tracks from Aliens and Backdraft have been very popular in trailers in the past. I know Jurassic Park had used parts of Backdraft in the original trailer.

If you want film scores just find the movie soundtrack on Amazon if not on I-tunes or other places on line.

You can try http://aresdownloadsonline.com