Hi. I'll be travelling in Thailand in august 2011. I'm not a resident of Thailand. How do I get a tourist visa to travel to Mainland China while in Thailand?

Why don't you apply for China visa in your home country? It is 100% sure that you can get a tourist visa to China in Thailand. If your application is denied in your country, you can go to Thailand to have a try.

If you really want to get a tourist visa to travel to Mainland China while in Thailand:
you need to submit the below requirements to China embassy in Bangkok:
(I) The original passport with a validity more than six months and enough blank visa pages;
(II) One copy of completed visa application form V.2011A in Chinese or English attached with one of the applicant's recent colorful front pictures of upper body (30mm X 40mm), you also need to fill in visa application form V.2011B
(iii) If necessary, application for travel visa needs the certification of the applicant's identity, round-trip (vehicle, ship) ticket or travel check or bank saving statement