[zxzax]

The copyright holders should just upload the sheet music to a different website. There is no requirement for anyone to redistribute a piece of Creative Commons content for free. That's true even with the NC licenses, in that case, the only real option for non-compliance is for the copyright holder to file a takedown notice to get the material removed. I know it seems counter-intuitive since you probably want to download that music, but this is what you're actually asking for.

If the copyright holders are absent then not much is going to be done about this -- that's one of the major reasons why artists join these large copyright holding organizations, to handle this stuff for them!