popular hasthe bookstore called "big bookstore" which is on the 3 floor of the building next to clementi NTUC has too. the bookstore called "Ever Green bookstore (Chang Chun Shu Ju)" which is on the 2nd floor of Ginza plaza has too. if you want to buy the cover better bring books with you to try different sizes for there are many sizes. apprx. 80-150 cents per piece (price depends on size). some are more expensive since they are so-called "made in germany" or "switchland" whatever.