L-type question

Hi there!
I'm a Thai citizen but study in the US. I am back in Thailand for the summer, will travel back to the US (Massachusetts) in August. I plan to fly to China in December.

As it will probably be more hectic doing my Chinese visa in the US, is it possible to apply it in Thailand that far in advance? If not, do you know any legitimate tour agency (or know where to find one) in the New England region that could help handle this?

Many thanks in advance.