Those store chains usually purchase products directly from the manufacturers in huge liquidation lots and have established ongoing business relationships with those companies. They may spend hundreds of thousands of dollars to over a million dollars in one purchase and buy by the semi truckload. I doubt that you have either the startup capital or business negotiation background to do business like that.
For a small startup, you'll need to take a different approach. While most big manufacturers will not deal directly with small operators at all, many smaller one do. You could start by looking up some local manufactures in the Yellow Pages, give them a call and ask about the possibility of purchasing liquidation lots from them. You would need a great deal of capital available and liquidation lots are usually by the truckload, so you will need plenty of warehouse space to store it.
An easier way to start might be to watch your Sunday newspaper classifieds for business liquidation auctions. These are conducted from time to time and you can often purchase goods very inexpensively and in smaller lots than by the truckload.
Another idea might be to find someone who is already in a small business in this field and partner with them. They may have the business contacts to acquire goods, but need help making purchases and such. Make sure you get and such agreement clearly in writing, though, so both parties know what is expected.