For some old books, you can find a seller on the Confucius old books website. The Confucius Old Book Network was an online platform for selling second-hand books. It had a large number of merchants and readers. You can search for books you are interested in on the website and then contact the merchant to ask if they can sell them. You can also consult the customer service of Confucius 'old book website to understand how to represent the old book business.