Hello deadpxlgames, I appreciate the interest to use the assets in your game! :)
Unfortunately, I don't have the songs in that format, since I made them in FamiTracker to run on NES, so I'd only have them in .nsf.
Converting the sound effects from .wav to .mod should be good, which are small files and I think a tracker like OpenMPT should play samples and convert to that format, unlike the entire songs, which would need to be rewritten entirely for GB format .mod).