Unfortunately, I think people struggle to find a dracthyr-only concept now that Dragonflight’s initial hype is over and done with. Which is a shame, I feel there’d be some cool draconic stuff you could do in a dracthyr-only guild - I just don’t have the time to lead one at the moment.
As for OP’s question, I only know of the Onyx Reavers that were recently made - whether or not they are still around, I’m unsure.