They're all over the place.

Niche, or very specific communities haven't taken off yet because things are still building. There's not been a need for a c/fordfestivamods because it takes millions of users to find ten people that even own one of the damn things at this point.

Breeds are a little less specific, but so far the generic dog c/s have been good enough.

But here's the real thing. Why don't you set one up? Seriously. Instead of waiting for someone else to do it, be the guy! You know your dog breed, you know your car. Start the c/ and guide other people to them! Help build this grand experiment that is the fediverse :)