I don't know much about the Newton, but I didn't want y'all to feel left out. So, I did some hunting around, and I found The PaperBack Page.
You can use the software available there to translate fanfiction into Newton format. At the top of each author's page in this website is a link to their home page. At that location, you can download their stories in text format and convert them to Newton format.
I was going to do this and make the stories available, but I simply don't have the disk space for a second version of each story. I also have no way of checking to be sure the conversion worked, and don't want to make available anything I can't be sure works. (Did that make sense?)