Seattle area has the nations largest and oldest grocery co-op - https://www.pccmarkets.com. 16 stores and generally doing well. The answer to how to keep it going is to run it like a grocery chain with experienced leaders and good board governance. In my experience a lot of the smaller coops I've seen have a problem separating the ideology from the need to run a business, grocery is notoriously low margin so a little waste is all that is needed to sink the buisness. Check https://www.ncg.coop/find-co-op to find a co-op near you.