This look's like the joker avatar I looked for month's ago. I managed to track down the creator (sorry don't remember the name any more) and he's profile said the avatar is no long avalible to buy. I think the creator has left SL but I'm not sure.
The one at Gotham City look's like this one, but not quite as good I think. I am still keeping a look out just incase, if I see it, or any good one's like it, I will let you know.