As a Us citizen, traveling in Buenos Aires, can I obtain a visa for China in Buenos Aires there?

Generally speaking, it is not hard for a US citizen to obtain a single-entry China tourist visa in Buenos Aires, if the two-way flight tickets and hotel booking are provided, it is possible for you to get a China tourist visa.
If you need a visa to Argentina, the valid Argentine visa is required. If you are exempt from a visa to Argentina, the entry record to Argentina is required.

I received an answer to my question of Sept. 20th, (Jared), which mentioned airline tickets and hotel reservations
I will be sailing to China on a cruise ship. Will the cruise reservations copy allow me to get a visa in Buenos Aires as an American citizen?
Jared

the cruise reservations copy and the travel itinerary of the cruise are required for your China visa application. If you disembark in 1 port within Mainland China, a single entry China visa is required, if you disembark in 2 ports within Mainland China, a double entry China visa is required, if you disembark in 3 or more ports within Mainland China, a multiple entry China visa is required.

I can only say that it is greatly possible for you to get a China visa, but I can't 100% sure you will get it.