I just joined the NZ lemmy here, because Lemmy.world was slow. This instance is much faster for me, but when searching for communities, many that I was subscribed to with my lemmyworld account didn’t show in the search results.
I fixed this by manually finding it in the address bar, like this:
https://lemmy.nz/c/linux@lemmy.world
And this will work for all communities, just replacing the appropriate parts:
https://lemmy.nz/c/[communityname]@[instancename]
Then you can subscribe and it will show in your ‘Subscribed to communities’ on the main page. (sometimes I have to refresh for all to show up).
This might be a known issue at the moment, but I’ve only been on Lemmy for like 3 days so idk
You can search for communities across many instances at https://browse.feddit.de/.
However, it looks like it just indexes Lemmy and not kbin.
There’s also https://lemmyverse.net/communities which is listed in the FAQ
Though I think the OP is about having trouble finding communities you already know about, where as the community browser is for finding new ones.