If it's a GBS you're looking for, you need to check out Knurek's GBS Penultimate Archive. He keeps it well updated, and is always on the lookout for more content. It's my understanding that if a GB song has been made/ripped (in some sort of GB format), then it's on that site. Take a look around. You might find something you like. Mouser X over and out.
The only thing I know of is - http://gsf.caitsith2.net/index.php?sortby=updatedd there is no penultimate GSF site but this is as close as you'll get. As for GBS - http://snesmusic.org/hoot/gbs/ - I'll still keep a lookout for Commander Kenn or I may rip it myself.