The Old Poster is one of the many collectibles you can find throughout the Pizzaplex. You can find this one a little ways into the game. Before you can find it, you will need to survive through the night and contend with some frightening animatronics. Here is where you can find the Old Poster in Five Nights at Freddy’s: Security Breach.
Before you can obtain this collectible, you will first need to make it to the daycare by getting the Daycare Pass. Once inside the daycare, you will need to deal with Sunflower and Moondrop. This duo can be a bit tricky to outmaneuver. After you get the power back on, you will be kicked out of the daycare and picked up by Freddy.
With the animatronics searching for you, you will need to stay inside Freddy or come back later when they are gone. When you exit the play area of the daycare, turn to the right to find the gift shop. Head inside the gift shop and walk to the back. There you will find a small hallway. This is where you will find the present that contains the Old Poster. You will have to hop out of Freddy to pick it up.