Be sure to tell friends and family that you are starting to clip coupons. Recycling centers are another good place. Locate your local centers. You will be amazed at how many people toss out their Sunday coupons. Many are happy to offer their extra inserts.
Convenience stores are another great option.
Many stores only need the front page of the newspaper for credit and discard the rest of the paper. Just speak to the manager. Magazines have a nice assortment of coupons. Try writing individual companies or even emailing them. I would like to be on your mailing list if you have one, so I can be updated on your products in the future or participate in any promotions or surveys you may have in the future.