Another place to find coupons is inside the packages themselves. Companies often include these. Sometimes the included coupon is advertised on the outside packaging but most of the time it's not. These coupons are a bit like finding the prize in the cereal box.
Sometimes coupons are printed on the box to be cut out. These are easy to overlook if you're hurriedly preparing dinner so be sure to keep an eye out for them.
Coupons almost always come with free products you receive in the mail.
A newer place to get coupons is electronically. Coupons codes can be typed in online, attached to a store's member card, or sent to your cell phone to be shown to the cashier at the register.
You could also gather those coupons is through trading. There are lots of people out there using coupons and it's inevitable that you'll get some you just can't use. If a friend has a baby and you have a dog you could trade your baby items coupons for their pet items coupons.
There are also coupon trains. In a train an envelope is mailed or passed from person to person. You take out the coupons you would like to keep, replace them with a like value of coupons you don't want and pass it along to the next person in line. Be wary of expired coupons if you decide to try trading.
You could also take advantage of a coupon clipping service. These are organizations that gather and clip coupons then sale you the ones you want.