One is over on feddit.de. It only searches lemmy instances atm, though, and idk how or how well it's updated as things are made. It seems to go by community name, so for example "drawing" does not return sketching subs and the first result under "art" is Star Trek.
The other is lemmyverse.net, which seems to parse searches FAR better. With the drawback that neither of those recognizes anything on kbin yet.
It's helped me here and there and apart from the drawbacks like the first one's behavior, I wonder if my (and @Treedrake 's) trouble is a combination of my own interests being niche and most of the people engaging in those interests being on mastodon instead of here. Fediverse Party and Fedi Directory both tell me there are sizable resources for what I'm looking for, just not through a forum.
This severely limits lemmy as it can't interface with mastodon tweets/microblogs, and hinders me as well until I have the ability to follow tags and see them in a dedicated feed.
This is one of those circumstances where forum and blogging culture don't really mesh well. The audience is present but already busy with their own thing, and we're expecting a different form of interaction than they are.