Rebecca,

here's the piece that I hope you hear: you are far better off building your own, because that gives YOU control over who plays in your sandbox, and you can never be invited out. You and I can wait to find the right group, or we can build it. It doesn't have to be a big deal. You already have access to a fair number of those potential folks right here on Medium. If I were you I'd start there. Send a PM to those folks, ask them if they would consider joining a mastermind group, see what they say. What do you have to lose? Nothing. As for duplicating efforts, honestly? Who else is doing this? WHO CARES? This is for you. This is uniquely your effort. It has nothing to do with anyone else's efforts. Duplication is a non issue. What you build is unique to you. Truth? Not many people are doing this. Whjy? because it takes work and passion and effort to build. If we want something better, different or exceptional, we have to build it ourselves. But that's just me.