Where do coupon websites find their coupons?

Is there some service that aggregate coupon promo code ? There is a lot of coupon websites out there, I would be surprise that all of them fill in information by hand. I didn't find any freelancer jobs for writing the code.

I couldn't find anything, any ideas ?

Either take it free from affiliate networks or pay for coupon feed services. There are many services that offer coupon feeds such as http://www.couponfeed.net/ and http://www.formetocoupon.com/. If you go the free route you may have to spend a lot of time cleaning the feeds so they give you proper deal descriptions, titles etc.

A lot of affiliate marketing portals offer coupon feeds for their affiliate programs.

For example, Commission Junction (www.cj.com), one of the largest, has a coupon feed available at http://cjbeta.com/offers/