can I apply for Chinese visa in New York

So you mean you want to apply for Chinese transit G type? You can apply for it from New York!
Or if your total layover time in PRC is less than 24 hours when you fly to Pakistan from USA, you can enjoy the 24 hour direct transit, in this case, you don’t need to apply for a transit G type.

Is there anyway way that I could get chinese l visa from newyork or mexico because in same ticket I can enjoy the visit

Yes, it's possible that you can get it, but you may need to provide an invitation letter from PRC Tourism Bureau to apply for the L type.

What is prc tourism bureau? Can you explain it and from where I can get it ??

PRC tourism bureau refers to Chinese Tourist Bureau which is in charge of tourism affairs and is responsible for the administration of domestic and international tourism policy making, execution and development.
You can find travel agency and ask it to help you get the invitation letter.