chinese visa for latin americans visitng Japan

We will be 9 days in Japan participating in a convention, and, on the way back to Latin America, we want first go to Beijing and do some tourism. I am Argentinian and my wife is Paraguayan, and both live in Paraguay. Paraguay doesn’t have Chinese embassy and is very difficult for us to obtain the tourist L here. Since we will be in Japan at least 7 working days, I wanted to know if we can get the (L) in the Chinese embassy in Tokyo during our stay. We already bought the air tickets to China from Japan, and are now looking for a travel agency in china which will get us the hotel and give us the tour (6 days).