Great threads and suggestions! @emily, I'm working on a guide right now that hopefully will make for some good first PRs— contributing to documentation. It sounds like you might be beyond that, but I know those were most of my early PRs.
In addition to the lists (such as the one you cited), and sites like First Timers Only, there are some really helpful resource rounded up in freeCodeCamp's How to Contribute to Open Source:
rOpenSci, like @nick mentioned, is a perfect place to look, but I do hope to build out an easier way for contributors and maintainers to find each other (in addition to tagging GH issues as being good for first-timers, etc).