AFAIK they should appear in the magazine (community) search if atleast one person from kbin.social has subscribed, and first people on kbin.social to find them are finding them through sidebars of magazines, comments, and browsing other instances.
It works great on instances where this whole federation system is not broken, and I strongly believe it will work great here too! We just need to be bit patient since a mass migration is occurring on this instance which is held up by one person, who is constantly working on making the site scale up to the demand.
You can browse the already "connected" to kbin.social communities (some kbin.social user has searched a specific instance, i.e. typed into the search all together: @ deathcore @ lemmy.ml) to search already connected lemmy instances you can go to magazines tab and type "lemmy". When federation works again, you should see all the communities that have been connected to kbin.social by typing the community name.
EDIT: seems like the normal search (search icon on top bar) finds communities better which have not yet been connected. The federation being broken hinders the search a lot, but I was able to make the first connection to @firefox by typing (all together) @ firefox @ fedia.io and it made the link. Now anyone on kbin.social will find that community in the magazine search.
About the fragmentation of communities: this happens but it can have its benefits. When communities settle some might become more concentrated on a certain aspect of the topic, and crossposting will occur too so you don't have to worry about subscribing to all of them. I know that on reddit for example the original r/TikTokCringe was a cringe subreddit, but with time it became a home for all tiktoks (cool ones too). Someone decided to make a real TikTokCringe subreddit that fragmented from the original one and so on. Both had healthy amount of activity. The original actually became a sub for cool tiktoks, and the newer one the actual "cringe tiktok" sub.
blackluster117