How to obtain product(apparel) catalogs from other websites(merchants)

I am in design phase of a startup(Not mine). Website uses power of crowds to select and recommend best apparel to other users of website. However to start with we want to have inventory where users can start voting and recommending to each other. Any Ideas where such catalogs for apparel can be found?

I know lot of merchants submit their catalogs to websites such as yahoo shopping and others but for a new website what is the best way to obtain them?