In China, Muslims are especially from the Hui people. As the Hui people mostly live in northwest of China, Muslim restaurants are common to see in the northwest, especially in Xian, Ningxia, Qinghai, Gansu and Xinjiang. In South China, there are not so many Muslim restaurants. As I know, there are some Muslim restaurants in Shenzhen and Hong Kong. However, it's just 'some', not 'many'. Thus, I think it may be not so easy for you to find it. I suggest you carry some Muslim food when you go to these cities.