Out-of-print books could be found in second-hand bookstores, online second-hand markets, collectible value websites, or libraries. 1. Second-hand bookstores: These bookstores usually put out of print books on the counter for customers to choose from. You can find these bookstores on your local secondhand bookstore website or on social media. Online second-hand markets: platforms such as Taobao, Craigslist, and Facebook Marketplace allow users to sell books to others. You can search for out-of-print books on these platforms and pay attention to prices and inventory. 3. Collection value websites: websites such as Confucius Old Book Network and the electronic version of the National Library of China usually sell electronic or paper versions of out-of-print books. 4. Library: Some libraries collect out-of-print books and sell them publicly. You can find information on the local library website or social media. It was important to note that the number of out-of-print books was very limited. It might be difficult to find a book that one liked. When looking for books, it is recommended to pay attention to some substitutes or updated versions of books to make a better choice.