Like MANY people have already said, there aren't many American/English doujinshi. (Holy cow, I spelt it correctly! FW007!) Though translated Japanese one's can be found online.
I remeber google-ing 'Yu-Gi-Oh! Doujinshi' or 'Yuu-Gi-Ou! Doujinshi' and found this girl's webpage who had about 10-15 different translated doujinshi's...
I recomend google-ing it and see what you fine. Also, use multiulpul serch engines and un-famous one. (I.E.: mama.com , altavista.com)
Yeah, I'd google it up for you but I'm lazy like that.
So yeah, happy doujinshi hunting! mrgreen