Honestly I think the best means for changing things is right under our noses: voting. Not just federal, but also state and local. As it is now, in most places tax cuts that flow mostly to the wealthy are still a great political move that’s an easy way to get votes. That’s the first thing that needs to change.
There’s all kinds of groups like the Center for Tax Reform and the US Chamber of Commerce that push for policies that tend to increase financial inequality - but as far as I know there isn’t one for reducing inequality. Given how many people recognize the problem, maybe there should be one. And then politicians can start to fear that group as much as they fear the others. Of course it won’t have a lot of wealthy donors, but as some politicians have shown small donations can do a lot.