Library's a solid place to start. Evelyn, the librarian, has been here longer than pretty much anyone, and she's been amassing information that entire time. Dipper and Mabel Pines have a collection of Wonderland-specific information as well, in Angel Investigations.

My own notes only go back about a year, but they are dutifully recorded in my Zine, the Shattered Mirror, along with references to anything earlier than that that seemed relevant. I'm happy to provide either digital or physical copies if you're interested.