I know what you mean about small fandoms--I'm still dismayed that Sky Captain fandom is pretty much gone. It started off strong, with some fantastic stories, and six months later was more or less DOA.

And there's been fandoms where no one else goes for a certain pairing, or some in which I'm only in the mood for gen but can't find much that isn't either het or slash.

Were I a more prolific writer I'd do something about that, but alas I'm not :-/