Instructions
Pet Supply
Push the "Go Out" button on your DS touch screen.
Press "Shopping" and "Pet Supply."
Select a ribbon you want by clicking on it. Choose "Buy" to get the ribbon. Ribbons are more expensive here than at the Discount Shop. However, it's easier to access the Pet Supply, as you don't need to take your dog on a walk.
Discount Shop
Press the "Walk" button on your DS touchscreen.
Draw a path on the screen that takes you by one of the two Discount Shops. They're represented by the buildings with dog bones hovering over them.
Walk your dog until you reach the Discount Shop. If you encounter a trash bag or brown box, whip the leash to make your dog run past it. Otherwise, he stops and eats, which can make him sick. To whip the leash, draw a forward slash with the stylus.
Select the ribbon you want and push "Buy" when you reach the Discount Shop.