There's also no centralised Lemmy site/index yet that centralises that information.
That's fine and all if you're looking for content on somewhere like lemmy.ml, or lemmy.world, but you might run into problems if you're trying to search for something that might be located on beehaw, or sh.it.just.works instead, which doesn't have the word "lemmy", and might get skipped.
You also have places like Kbin, which don't get captured in a search at all, both because they're not lemmy, and also because they don't contain the word lemmy, which doesn't help if you're trying to search something that you thought was on Lemmy, but is in fact on a Kbin magazine.
Unless it's using the Registry for some config values.