There are many shops specializing in selling brush Xuan paper, and the prices vary according to the quality. If you want to buy low-priced pens, paper, inkstones and ink, there are also top-grade inkstones (more than one store in that street sells these things, you only need to walk west from Dashilan in Qianmen to Liulichang West Street and you will find many stores selling them).
Ji Xiaolan often went to Liulichang to buy these things during the reign of Qing Qianlong, so this street is the first choice for you to buy these things. Including the rice paper and brush I bought there when I practiced calligraphy.