@mitchgillogly we built a tool to help with this called Ship. Our goal is to make it easier for makers to start building an email list and community/gather feedback from interested people. Many people use this to manage beta testers.
That said, you mostly still need to find the people yourself, which I realize is challenging. At the highest level, I recommend clearing mapping out who you're building for, find where they hang out, and do everything you can to introduce your "solution" to their "problems" without being spammy.
Also, take a look at this blog post about Building in Public. It might be useful.