OP, I have sympathy for your situation. One of the best intro texts I read about SJWs was on a death metal site. You guys get this, and you deserve our support.

Here are some things I'll suggest:

• Boycotting would have been the most powerful tool, and you know this, but for your own reasons, you don't want to do this. This is fine.
• A direct email campaign, both to the service provider (Bandcamp) and to its advertisers/partners/affiliates should be started. Get contact info and an outline out through your social media channels and get your fans to write, write, write.
• Get some posts about this out on news sites and blogs that are sympathetic to your cause.
• Try to get a hashtag established, through which people can find each other. #MetalGate works, I've seen it in the wild since winter 2014, or something else.
• Read Vox Day's SJWs Always Lie to learn in detail exactly what you're dealing with. A free excerpt is available here.

Good luck.