Because after all clowns are freaking WEIRD. Not like catgirls or 50 foot women, or 50 foot women with busts that crush mountains or people shrunk down to be scared of mice and bugs and all. Yeah, that's all normal, but clown TF? Too out there for us. 9_9
This artist has some fun clown stuff-
http://www.furaffinity.net/user/pravusbelua/ Though to warn, she has other interests, but I found one or two clown bits.
This artist has one or two poof TFs in addition to the page-by-page above-
http://luckybucket46.deviantart.com/
Mostly though, you're gonna be browsing yahoo groups and those're kinda sporadic.