Chapter 5: There are three playboys in this chapter, although they're not in the same positions as the demo. Note that they are all tied to the brewery assassin though.
Playboy #11 is above your starting point with the machine gun. When they run downstairs, go upstairs and grab the playboy magazine lying on the floor.

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Playboy #10 is on the first floor of the brewery. It's in the office on one of the racks. Grab it after you cleared the floor. Note that the office is basically sealed off by the fire on your way out, so grab it now.
Playboy #12 is just past the fat man on the fourth floor. After he gets killed walk past him and look at the back corner. Pick up the magazine while Joe picks up Harry.
Chapter 6: It sems that a few playboys made it into prison. There are 3 inside.
Two are in the prison yard. Make sure that you don't go to Leo's position, since that makes you leave the yard.
Playboy #13 is off to the right side of the starting point. It's behind a small bleacher to the right. Look for the sleeping prisoner on the ground.
Playboy #14 is just off of the basketball court. Go across it and look for the big shed. There's a little niche on the far side of the shed. Grab the playboy off of the ground.
Playboy #15 is in the laundry area. When you go in for the fight on your work day, just win the fight. Before you talk to the guard, look to the left side. It's sitting on top of a sink/washing machine.
Chapter 7: There are playboys in this reunion chapter and one involves one heck of a drive.
Playboy #50 is at the top of Joe's apartment building. Don't just follow him out. Go up the steps until you reach the top. Grab the playboy.
Playboy #17 is literally right in your path. It's on an end table on the second floor of your new apartment building.
Playboy #16 is a tough one. It's all the way over at Harry's Military Surplus store. I don't believe it's there earlier (post in the comments if I'm wrong). When you get the car to go buy a suit, make the long drive and go inside. Walk down the steps and pick up the playboy. It's at the foot of the steps.
Chapter 8: There are four playboys in chapter 8.
Playboy #19 is in the foundry. It's after the first cutscene when you move past the blockade of cars (and one tries to run you down). Move to the shack on the left and look for it on top of a drum.

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Playboy #21 is also in the foundry. After you fight the first group in the new area, move forward to the corner and follow the tracks. After the tracks end, watch the left side for a playboy.
Playboy #20 is the one you'll probably miss. After you pick up #21 and officially end the battle, walk toward your allies at the gate, but don't go to them and trigger the meeting. Walk to the left under the stairs and into the little camp. It's under the cot in back.
Playboy #46 is potentially on your kitchen table when you go back home after the mission. Note that some players have reported seeing it after they came home in chapter 7 (Skipping the cutscene ending the chapter for me, so I'm not sure).