Initially from Margo Roby. The Found Poetry Review, run by Jenni Baker, had an annual found poetry challenge that I joined a few years ago. 2014, I think. Jenni passed away last year from glioblastoma, and the previous participants decided to keep it running but only in October. It’s a private group on Facebook, The Poeming. You’re assigned a book, and that’s your source for the challenge. If you search The Poeming on Facebook you can ask to join the group, maybe drop a note about to admin to be included.