Mystic Mine is a nice indie game that was open sourced in 2012 under the MIT license, but has IMO not received as much interest as it should.
The graphical assets are also open source under the MIT license (though it's not really appropriate for art assets, an issue has been raised for this).
The sound effects and music could have not be freed with the rest of the game, so they were replaced by silent placeholders.
I have opened an issue to list the sound files that need to be replaced: https://github.com/koonsolo/MysticMine/issues/12
The list is not so big, so I think we could manage to find some good replacements as a community effort and make some pull requests.
The old Mystic Mine website seems down, so I'm not sure the original nonfree version can still be bought to use as a reference. On the other hand I found a link to the old demo page, so the demo can still be downloaded: http://www.koonsolo.com/mysticmine/demo.php
Here's a video of the old demo version with sounds and music:
youtu.be/SQ6CMhuuxUc