you can apply for a Chinese visa at Consulate General of China in Chiang Mai or Chinese embassy in Vientiane, however, the visa regulation varies according to your nationality and other events, maybe you can get Chinese visa in Chiang Mai or Vientiane, it is not 100%, you have to have a try. Sometimes, even though you hold valid visa or residence permit of Thailand, you can't get a Chinese visa in Thailand. For more information, you can refer to https://www.travelchinaguide.com/embassy/visa/application.htm