In my experience, the big stores won’t even put you in their system as a vendor unless you have a large range of products to sell them. You are best off finding a distributor or manufactures agent that represents a range of products in your category and already has connections with the stores you want to sell to. As mentioned before, they will expect a LARGE cut of the profits. This process can take years, so you might as well start selling to the smaller stores while you work on getting in to the bigger ones.