Check out this blog post by a coworker:
It describes a command line tool (cross-platform, so it will work from Linux, MacOS, or Windows) that pulls random projects that are receiving pull requests. The whole process is documented so if you wanted to tweak it to search for other types of projects (for example, Node.js instead of .NET) it should be straightforward. You could even get started by submitting a pull request to this tool that passes in a flag to choose technology stack, for example.
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