Nostr.watch has a list of all relays but it doesn’t define them by the content posted, probably because most relays are just for anything at all rn. I’d be surprised if someone didn’t have content specific relays by now though.
Discussion
Having browsed the welcome relay for a bit, I think content -finding is of major interest (and not just to noobs lol), not specifically re: relays but it's interesting that there is a desire to seek. I was saying this earlier somewhere also that part of the joy of nostr is finding and digging for content.
I am also under the impression (might be wrong, I don't know much) that it is possible that private relays already exist but wouldn't necessarily be known. Which is curious to me.