You can't find one because there isn't one. And there probably won't ever be as we don't need or want one. People participate here because the level of discussion is the highest of any webmaster community. We don't need monetary incentive to participate. We're here because we get to learn and discuss interesting topics. Forum that use revenue sharing do it because they are desperate for members to participate. That's definitely not an issue here.
And, even if SitePoint did offer revenue sharing, it still isn't worth it as there is no money to be made. The feedback from users at forums that offer revenue sharing is that you don't make any money. It sounds good in theory but in reality it just isn't worth the effort.