Dan Clore, founder of the Robert Anton Wilson Fans group on Facebook, points to a couple of his books. Weird Words: A Lovecraftian Lexicon is a reference book; Clore explains, "Dictionary of horror/fantasy diction, with a large selection of sample quotations illustrating usage. Authors quoted include Edgar Allan Poe, Arthur Machen, A. Merritt, H.P. Lovecraft, Clark Ashton Smith, Robert E. Howard, etc., but there's also plenty of quotes from writers including Aleister Crowley, William Burroughs, and plenty of Robert Anton Wilson.
Should be especially useful for those interested in RAW's connections to the Cthulhu Mythos."
The Unspeakable and Others is a collection of Clore's writings. There doesn't seem to be ebook editions of either of these.