How to find a local American travel agency to travel with a group to South America?

This is very simple. You want to find a local travel agency in America. There are many travel agencies founded by Chinese in the United States, which are specially designed to facilitate China people to travel there, and there are also special channels in China. I'll just list two big ones.

Tufeng Travel was acquired by Ctrip's China Travel Agency.

China Travel Agency acquired by Nami Tourism Tuniu

These two travel agencies are well-known Chinese travel agencies in America. You can visit them on the official website.