It's possible you're thinking of:
* Mark Twain Media, Inc.: A publisher of educational resources for teachers and students. Their website is [https://www.marktwainmedia.com/](https://www.marktwainmedia.com/).
* Mark Twain Enterprises: The organization that manages the rights to Mark Twain's works. They have a website, but it doesn't focus on publishing.
Please clarify if you are looking for something else.