Can you tell me where I can apply for one time visa to china ?

I hold New Zealand Passport. I got single entry to china.I booked flight ticket at 11/04/2014 from Auckland to Shanghai, and return ticket at 2/05/2014 from Shanghai to Auckland. It is alright . But Between these period, I am going to Japan three days. It is Tokyo or Shanghai? I still want to use my air ticket back to Auckland. Many thanks.