In Carl's video, he got the rarest animal treats from a bird tree, at which point he went bonkers with the bird trees. But I've always gotten all my golden and midnight treats from rabbits! Whichever you get them from, it seems you need max friendship first. Also Carl says you can spam the same interaction over and over, to max friendship-- not what I'm seeing! When I do it, I start getting negative reactions. You do seem to get better chances of positive reactions if you have the Animal Enthusiast trait.