Costco does sell grass fed beef.
An example of grass fed beef that Costco sells is Pederson Natural Farms 100% Grass Fed Organic Ground Beef.
Costco beef is mainly sourced from the United States, although some of Costco beef and meat products are sourced from other countries such as Australia and Canada but not China.
Costco focuses on sourcing of their beef from farms which treat animals humanely and process the meat in clean environments.
A significant portion of the beef that Costco sells is sourced from U.S. farms, and most particularly farms in the San Joaquin valley of California.
Costco also sells Canadian beef which is known for it's quality.
Australian beef and Angus beef is also a source of beef for Costco.
Costco does source some of their products from China which includes some various food items but not the beef.
The salmon that Costco sells is sourced from Norway, Alaska and Chile.