Japan has a huge marked for transgender fiction and erotica. Indeed, it seems the theme permeates all types of media: stories, movies and comics.
The female to male crossdreamers have their yaoi subculture, producing comics about gay male relationships, many of which are pornographic in nature.
Their male to female counterparts look for gender bending anime (animated movies) and manga (comics). One sub-genre of manga is hentai, comics with explicit depictions of sex.
I have put up two posts on Japanese hentai over at Rebecca’s World:
Japan, the empire of transgender comics.
More Erotic Gender Bender and TG comics Made in Japan (Hentai Manga)
Transgender Fiction, Captions and Comics 