@Vanessa **************
Here's what I would do if I were you:
1. I would do a search on Google (or Baidu if you're in China) for "Volunteer in Phuket". If you're using Baidu and not Google, you will have to spend some time going through the links. If you can access Google, use that search engine.
2. Find a list of volunteer organizations that interest you, and find their e-mail address.
3. Send them an e-mail that says something like "To whom it may concern. I am [name here], and I'm interested in volunteering with your organization. I'm currently in China. Do you issue Non-O visas based on volunteering to foreigners?"
4. Wait for responses. Get people's opinion and see which one is best for you.