There are some fediverse listing sites out there, including one that maps old subreddits to where the community has moved to in the fediverse (includes kbin and lemmy); but these actual services are not quite to the point yet where they have much discoverability built in.

It’s on the roadmap for sure, but as stated by the lemmy devs, the sudden influx of users has revealed many bugs, including some related to scalability, and for the time being they’re focused on that just to make sure the whole thing doesn’t collapse under its own weight. They’d rather have something working that isn’t complete than to focus on new features but everyone leaves because it’s crashing every few minutes.