At the moment, the only tool I know is available for that is https://browse.feddit.de. It should be officially endorsed by the project and available on join-lemmy.org, imo. It crawls the network and allows you to search for communities and see where they are hosted!
As for CAPTCHAs, Lemmy does not use any third-party provider, but rather a little library that generates them given a set of noise functions to apply. I'm not entirely sure how effective the top difficulty ones are at stopping OCR bots and the likes, but they seem pretty good.