What is the name of the book where the secret piano score is located? Where can I sell it in Beijing?

Let's just call it "a secret I can't tell." I threw my bag away … I forgot, but it should be easy to find. More than 30 yuan, the one who sent the novel, 12 bookmarks and piano scores! I bought it a few months ago. They are sold in big bookstores ... and golden keys, Xinhua and so on. I can't order it That novel should be written by an amateur. It is very watery, but the piano score is good and complete.