Hi
I found this page that has a few midi files for music boxes, they seem to work with Music Box composer:
http://sky.geocities.jp/mikann_nk/midibeya.html
There are other pages around with more midi files for music boxes but with no terms of usage I'm not sure it's appropriate to post, but this site above says this on another page regarding usage (translated by google):
① "personal hobby range" if your freedom to. I do but "redistribution" not to ♪
Use as ②MIDI data is also allowed, but practicality is not probably.
② direct link prohibited.
jtp