The prequels contain a lot of tracked music. This means that although all the music Williams composed for these films was never released it may be possible to construct isolated score tracks. The Episode I "Ultimate Edition" soundtrack is comprised of 2 CDs that feature basically an isolated score cut into audio tracks. Someone who has that soundtrack and the ability to do some decent sound editing should be able to put together an Isolated Score for Episode I quite easily. The other two might be quite hard if not impossible.