If you'll ever need music or sfx for your gb-ROM, I maybe could help out.
I do music with gb tracker (and others) which is able to put out z80 assembly data.
Here are some examples, if you want to hear.
My latest release came as a gameboy cartridge, the free ROM version could be found here. (Could also be found on gamejolt)
My musical collection on bandcamp.
As download or as a stream.