the best way to apply for a tourist visa whilst travelling?

hello,
I am planning on visiting china on the 1st October as a tourist. I understand from looking at various websites that I am unable to apply before 3months before I travel. My problem is that I am leaving in June to travel to various countries before flying to China, I will be a tourist in these countries. Will it be possible to apply in another country?
The places I will visit will be the US, various countries in South America and India? What documents would I need to produce?

Any information would be appreciated!
Thanks