Yes, I suggest you find a rep firm that has established relationships with these and other major retailers.  Not only will they help you get your product into the stores, they can be invaluable when it comes to providing guidance about everything from pricing to packaging.  Bear in mind that you'll need to pitch your product to several good potential representative firms and it may take you a while to find one willing to help that will give you, a new manufacturer, the attention you deserve.  But hang in there until you find just the right match.