There are some very knowledgable people out there that have shared their writing equipment expertise through their websites, books, e-books, blogs, etc. The following is an abbreviated, but ever-growing, list, of collectors, experts, sellers, dealers, and reference material that I've stumbled across, or connected with, while building the collection.
The KB Collection of Pencils - The Ken Bull Collection of Pencils book provides a detailed history of the mechanical pencil. It also serves as a catalog, showing the collection at its finest.