The people behind Humble Bundle were indie developers themselves, they were already established in the industry so they had their own games to use (which were popular) and had industry connections.

Right. The solution is to go make friends in the industry.

Consider a change in perspective - instead of asking "how can I make Humble Bundle model stick with my target audience", ask yourself "what can I do for my target audience that generates obvious value?". Hang out with the bands, hang out with the listeners, keep looking for other important players (labels, radio stations, venue managers, event organizers, government employees driving "persevere out culture" type of programs, politicians who are focusing on culture, etc).

If you spend enough time with the crowd and keep an open mind about it you are guaranteed to find something you can add to the table.

I think you've internalized a too-specific rule. Translate "bands won't give me their music if I don't have a big following" to "bands won't give me their music unless they trust me to do right by them and their music." Having a large following among people the musicians want to reach is one way to earn that trust. There are others.