First, there are many large clothing wholesale markets in Beijing, including Dahongmen clothing wholesale market, Zoo clothing wholesale market and Yabaolu clothing wholesale market. Judging from your situation, I suggest you choose Dahongmen clothing wholesale market first (Dahongmen clothing wholesale market here is a large area, including the whole street from Bai Rong World Trade Center in the north of Muxiyuan Bridge to Dahongmen Bridge in the south fourth ring road).
Second, if you want to find a representative clothing store in Beijing, you'd better go shopping by yourself. I suggest you go to Xidan Commercial Center. There are all kinds of grades, such as high-end shopping malls like Saite, and some small shops on the roadside are also good, giving you a wide range of choices.
Finally, I wish you a happy shopping. If you need any help during your stay in Beijing, you will be happy to help (at your own expense, hehe).