Playmate 25: When you reach the hotel garage, Joe will stand around waiting for someone to come and open the shutter door. While he's doing that, wander off to the left of the locked door to find the one that's wide open.
Once you're through, immediately hang a right to enter a hallway full of industrial dryers, then a left at the next doorway. Walk forward a bit and you should see this office doorway to your left:
Go through that and look to your left. The chapter's first issue of Playboy is sitting on the corner of a desk at the far end of the room.
Playmate 27: After Joe's installed the bomb, you'll be prompted to follow him up a stairwell. Go down it instead.
At the bottom, you'll find a metal gate blocking the way. The next issue is lying next to it.
Playmate 26: Before you hit the switch to bring up the window-washer platform, look to its right. You'll see the next issue lying on the floor, partially hidden by the railing.
Playmate 48: When you've finished up at the hotel and gone back to Vito's place, take a look at his bathroom floor next to the tub. It wasn't there when Vito left the house at the beginning of the chapter, but the next issue of Playboy will have magically appeared.
Playmate 47: When you're sneaking around the house with Leo, head through this door next to his desk:
You'll see the next issue on a windowsill facing Leo's front yard.
Playmate 29: Immediately after grabbing Playmate 47, head through the door into Leo's bedroom. Then go through the door on your right, after which you should head left and open the door to the bathroom. The next issue is sitting on top of a hamper opposite the door.
Note that if you get caught while you're poking around, you can either "retry mission" to restart in Leo's office, or just let events play out for a chance to freely explore the mansion.
Playmate 28: As you enter the apartment where Vito confronts Eric, you'll see a door across the hall from the front door. Open it and go through.
On the other side, you'll see a passed-out guy with magazines piled around him. The next Playboy is between his legs.
Playmate 49: Once you've arrived at Joe's newly redecorated pad, take a look next to his bed. The next issue's on the floor alongside a couple of other magazines.
Playmate 30: After you've gunned down all your enemies at the King of Tara pub, walk through the swinging double doors at the back of the place, next to the bar.
You'll find yourself in a dead-end hallway with the next issue of Playboy lying on the floor.
Playmate 33: Right after the shootout begins, you'll run up a staircase onto a catwalk. Head into the narrow hallway the catwalk leads into, and you'll find the next issue lying on the floor to your right.
Playmate 31: After the shootout in the warehouse, you'll find yourself on the loading dock. Turn left and head down these stairs:
Hang another left, and you'll head down this alley:
At the end of the alley, look to your left. The next issue will be hidden in a patch of weeds next to an overgrown dumpster. (You can also find this one at the beginning of the stage, when you're being led to the deal.)
Playmate 32: From the loading dock, head toward the center of the courtyard and turn right after you pass the semi truck.
Head straight past the gas pumps, and you'll see a container truck parked next to another loading dock. The next Playboy is lying just behind it.