http://www.anime-sharing.com/forum/anime-osts-41/single-tvanime%5Bsouten-no-ken%5D-ed-single-kokoro-no-rhythm-tobichiru-butterfly-%5Bdoa%5D-490573/
That's the closest i could find, but that's dead.
https://www.amazon.co.uk/SOUTEN-NO-KEN-ORIGINAL-SOUNDTRACK/dp/B003QXYFIG...