internet archive has a LOT of free ebooks/PDFs, especially public domain but also just lots of older things, even textbooks and picture books. amazing resource
i would go thru any libraries you can access first (for ethical/support yr library reasons) - most libraries have a form or you can go to the front desk to request a book be added to the collections. this works for ebooks too! it’s not a guarantee, but sometimes they say yes
if all else fails, you can also just google “[book name] PDF” and if it’s an older or popular title it will probably be online lol. and if you have ibooks you can then export the pdf to ibooks
