I want to know how to get discount coupons of big brands(pizza hut, domino's,Levis,nike) for my online store?
You can sign up for newsletters and affliate programs. That is the best way to get coupons and also get commission for each sale.
the best affliate site i use is http://www.cj.com (commission junction) they also have a lot of big brands as well. And most brands have coupons codes or discount links :)