There is a commissioner who just goes by "ehh123" who commissions many reverse TFs that are up all over the net. There are a bunch on transfur (here is the most recent:
http://www.transfur.com/Users/Lucern7/Submissions/18051 ) but they are hard to find without spending a lot of time digging because transfur has no reverse tf tag nor is their any way to search by commissioner and ehh123 commissions many different artists instead of just one or two over and over again.
Little Napoleon has done at least one such reverse TF piece here:
http://www.furaffinity.net/view/3551366/ ... possibly more though I am blanking on them right now. I know I have seen them, but they are rare and really hard to find again once passed over.