The list of locations below includes where I've taught with the wrong visa type for at least a semester, or was offered the chance to do so, or where I know for sure other foreigners have taught with the wrong visa type, and got away with it too. Locations in bold are those where the employer/ prospective employer is in the private sector, but not a language mill. The other locations are where the employer/prospective employer is in the public sector. The visa types are F, L and X:

Guangxi - Nanning
Hebei - Handan, Hengshui and Shijiazhuang
Heilongjiang - Hegang and Jixi
Henan - Zhumadian
Hunan, Xiangtan
Jilin - Changchun
Inner Mongolia - Baotou and Hohhot/ Hohhot
Shaanxi - Xi'an
Shandong - Jinan and Linyi
Shanxi - Jishan, Linfen, Ruicheng, Taiyuan and Yuncheng
Sichuan - Deyang, Hejiang, Luxian, Luzhou and Mianyang