Sometimes though the trailer music is not even part of the soundtrack. And if it is a song without lyrics it can very hard to find.
The original dragonheart movie had a beautiful soundtrack with a very emotional symphonic piece. It was part of the movie and the trailer...but then I started to hear it on every other sad trailer

From "The emporer" to "mulan" lots of trailers started using it. In that case, you just have to get lucky and ask the right person where to find the music.
And it looks like it worked out just that way for you too
