Food doesn't show up in the grocery store by magic. The food flows from farm, ranch or processing plant through a system of food distributors. Some large stores like Walmart and Kroger own their own food distribution networks. Others use independent networks.
Independent Grocers Alliance (Profile) Independent Grocers Alliance (IGA) is a cooperative that offers store franchising and distribution services.
United Natural Foods (Profile) United Natural Foods is a distributor of organic foods. In 2018, they acquired SuperValu which is a distributor to chains and independent grocery stores.