I've read some stories, but the best one found is the one where Microsoft bribes some Nintendo characters to join them.
There aren't enough stories, FanFiction.Net is dominated by Anime fans. You can tell because they like using Japanese words a lot. I have never seen so much usage of "Kawaii, Ai ****eru, and Yaoi" anywhere else on the net! Not even Japanese websites!
Although, the SSB place may have a small number of stories, but those stories are great! And Zelda has a decent number.