A good place to get Pro Plan printable coupons is at Dog Food Coupons. This is a coupon site specifically meant for dog food and no other products. Another good option is to use coupon sites like Coupon Sherpa and Coupons.com.
To look for Pro Plan coupons at Dog Food coupons, use the search bar, or click on Purina from the list of brands on the right side of the page. This brings up all Purina dog food coupons, including a variety of Pro Plan ones. At Coupon Sherpa, there is a search bar to type in pro plan. Click on Printable Coupons to view only these types of coupons, instead of deals or sales by Purina. Coupons.com has a variety of coupon codes, printable coupons and special offers.