I've seen them in every city, I think, but they do seem to be rarer since showtime. Maybe they are more common in some cities than others? I played [a certain city]* for quite a while, and they seemed fairly plentiful. But then, this was just before I got showtime.
Maybe their numbers got adjusted with the patch that came out after Showtime, rather than with the actual expansion itself.
*Name withheld in case I am stragetically insensitive again. Sorry, I know that phrase looks kind of dorky in context.