The Lemmy server finders operate using the Lemmy stats crawler tool. It maps the entire known network by taking a list of known instances and recursively querying all of the nodes each instance is federated with. The Lemmy stats crawler would be able to map Kbin instances as well if the API endpoints for retrieving instance and community information are the same between Lemmy and Kbin (which they're currently not, but I think Ernest is working on making them compatible). A temporary solution to find Kbin instances is the-federation.info's database which crawls all Fediverse instances using generic ActivityPub endpoints, but it cannot show instance details.