Most stores (except Walmart) have them on their store apps. Kroger is the one I use most frequently, and they have hundreds of digital coupons.
Coupons dot com also has an app that has dq's.
@Luuluu You can load them to your store card (for example I have digital coupons from Shoprite) or you can go to coupons.com on your desktop to print coupons (sneaky hint - if you store doesn't require color copies, print in draft and black/gray to save ink) or use the coupons.com app (link to your paypal and be directly reimbursed when you upload the receipt)
Where do you mostly shop?