Alrighty well... I'm going to start a post with some links for books and patterns that have been recommended to me that are out of print. I have a post about the legality, but apparently for individual patterns it's legal.
Some but not all books can be found in various places like the internet archive or Anna's archive. Use your own personal discretion. My intention is to put together some easy to access sources to help people, and that's all.
If you would like to contribute a pattern, let me know. I would like some basic information like the creator and name of the pattern if it's not included in the document. Just so I can properly label things at least.
If you want to suggest books I would also welcome that! Any book or resources you think are super useful but are no longer for sale. I was looking at lists of knitting book suggestions on a couple Reddit posts and noticed a fair amount of the suggestions were out of print. Thus... My idea to collect these resources.
Philodendria by Lavish Craft
Arc of the Hypotenuse by Lavish Craft
Cozy Autumn Sweater by Renardo Endormie
Circle of the Fae Mushroom Mitts by Sophie Skinner
Katia 6183-17 by Fil Katia
Amanita keychain by Lilia Levchuk
Frosted Ornaments by Rae Blackledge
Snowy Owl Pillow by Steph Lewis
Mirkwood Mitts by Elfmoda
Northern Lights Beanie by Amanda Foster
Star Dreamcatcher by The Chilly Dog
Knit to Fit by Ida Riley Duncan
Reader's Digest Knitter's Handbook by Montse Stanley
The Complete Book of Progressive Knitting by Ida Riley Duncan
Elfmoda Maple Leaf Shawl - Knit and the Ravelry
Puzzle Piece Blanket by MeganMME and the Ravelry
Ulita by Alla Chikalova (Алла Чикалова) and the Ravelry
Elfmoda Maple Leaf Shawl - Crochet and the Ravelry
Star Spiral Blanket and the Ravelry
Night Moth by High Crafting
Day Moth by High Crafting
Size Inclusive Collective - knitting and crochet patterns for plus sizes
Antique Pattern Library - useful for all sorts of things