If you do just want to make music then +1 to Localhorst86 as LSDJ (
http://www.littlesounddj.com/lsd/ ) is indeed the gold standard here.
If you mean like the sappy stuff for the GBA and the SDAT stuff for the DS commercial games then no, not really. The GB/GBC saw some standardisation of file formats and such but nothing as extensive as the previously mentioned systems and a lot of devs did their own thing.
Some games might have individual programs for them, pokemon being the first place I would look to see if I could find such a thing (if nothing else I think red has a complete disassembly and that will include all there is to know about the music, though I don't think it will be necessary to approach it from that angle). Some other games might have had their formats individually looked at. You may even be able to operate at "I has midi, want insert so plays in game" level.
http://www.romhacking.net/?page=doc...=&perpage=20&level=&title=&desc=&docsearch=Go has a few things for some unreleased games and
http://www.romhacking.net/documents/689/ for a collection of games from one dev/publisher (such groups often reuse their old work between games).
I don't have anything special for the GB/GBC audio like I have for the GBA (
http://belogic.com/gba/ ) and DS but
http://problemkaputt.de/pandocs.htm#soundcontroller should get you somewhere if you do head down the path of learning hardware, though combined with the unreleased game stuff above you should be able to get an appreciation for what goes and some of the practical considerations.