....Neville/Bill would be a rare pair in my opinion. And I am not basing it off the statistics you just gave me either, fyi.

Looking around at deviantart/LJ/ff.net, I'd say, that while it is small-ish, Neville/Ginny has a large enough fanbase for it to be not rare. I'm sorry your community isn't super active, but it seems to me as an outsider who doesn't take an invested interest into any particular pairing that there's enough strength there to call it a middle-of-the-road pairing, not a rare one.