Unless you plan to either use only Sierra's music, or find midi files on the web for use in your game, you may need to create some fresh new sounds from scratch. Anvil studios is the perfect tool for the job.
Offering several tools that are well over my head, the different composing environment options make it easy for anyone to scratch out something. Offering piano keys, a guitar fret, or my favorite a piano roll as an interface for composing the sounds or music it makes it easy to click around finding just the notes you want. At least for those of us who are not musically inclined.
You should note, anvil studios creates midi files and that type of file itself is not usable by the sci interpreter, you will also need Ravi's tool
SoundBox to convert your freshly made midi sound into a sound resource that you can use in your games.