Since the closing of Russo’s market in September 2021, a group of people has been working to create a new option for grocery and food shoppers in the Watertown area. On June 15, the Charles River Food Co-op formally kicks off the sale of shares in the planned store. The co-op had a soft opening in early June, and has already sold more than 70 shares, said Nick Quaranto, interim board president of the Charles River Food Co-op. The money raised by the shares, which cost $200 each, will go toward planning and building a store in one of the communities on which the co-op is focusing: Watertown, Waltham, and Newton. Shareholders will also be able to participate in co-op elections and will receive discounts after the store opens.