According to the Hell Fire Book Readers’ Club FB thread: “The Book Of Forbidden Knowledge was published in 1951 by the Johnson-Smith Novelty Company (X-Ray Specs and Joy Buzzers, anyone?) The section titled ‘Secrets of Black Magic Revealed’ is actually copied verbatim from the 1725 grimoire The Egyptian Secrets of Albertus Magnus…”
You can DL this tome here: https://archive.org/details/TheBookOfForbiddenKnowledge
Meanwhile, here’s an online archive with a buncha grimoires posted f’r free: https://www.grimoire.org/
