It's often very difficult to get permission from the copyright holder for things like this, that is why most skin authors don't bother and prefer to make their own skins from their own ideas.

But it's fan art!! Doesn't fan art counts anymore??

First of all, just because someone views something like this as fan art, doesn't mean that the copyright holder will see it that way. Many many people have been sued because they published "fan art" without the original artist/author's permission.

Second, it is one thing for you as an individual to decide that you want to create fan art. But to ask another artist here to do it for you is asking them to decide to ignore the potential copyright of a fellow artist. Why would they want to do that, when they as artists themselves want the rights to their own work to be protected by the same laws? Not to mention the amount of work that it takes to create a skin that would potentially get them in trouble.

That doesn't mean that all fan art is illegal, or even unacceptable at WC. If you want to create something and submit it yourself, feel free to do so. Some fan art is accepted here. But it's not very often that you're going to find a skinner that will tackle something like that without permission of the copyright holder.