The Society of Archivists
Before the Fall, I believe The Society of Archivists to have been private collectors of rare books and antiquities, librarians, history buffs, researchers, museum curators and the like.
Since the Fall they have banded together and gone underground in order to keep their libraries and collections safe, especially from those that would burn, despoil, or otherwise use the knowledge found in their holdings for their own purposes. As all public research collections and libraries have been burned or destroyed, including most of the printing presses and offices (probably by Purifiers), and that books, newspapers, and magazines are no longer published at all, for fear of becoming the targets of some violent faction or other, it makes sense that The Society of Archivists has become extremely secretive and exclusive. It remains to be seen whether their insularity will truly protect them.
I have it on good authority that the collections are being sifted through by members of the Society in order to gain a better understanding of the events leading up to and surrounding the Fall, as well as other ancient, esoteric, and arcane knowledge for the use of the members. I fear that their greed for knowledge could lead to their downfall.