Technically, you should have 2 new tables. A table to keep the store information, and a table to contain the relationships between products and stores. As you are on v8 you can create a table called 'Store' and 'ProductStore', but you couldn't do this on v9, because there are already tables called 'Store' and 'ProductStore'.
Code:
CREATE TABLE [dbo].[Store](
[StoreID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](100) NOT NULL
-- any other extra column data you need in here
) ON [PRIMARY]
CREATE TABLE [dbo].[ProductStore](
[ProductID] [int] NOT NULL,
[StoreID] [int] NOT NULL
) ON [PRIMARY]