• I had to dig through the game files to find the majority of these locations. I can 100% confirm this is all of them.
  
• This achievement requires 10 full playthroughs where you collect a coupon each time. It might be possible to do 5 playthroughs, collecting 2 coupons each time, but I haven't tested that yet.
  
• Only TWO coupons will spawn per game...technically. See the next point.
  
• Every time you reload a checkpoint or die, all the items in the game (besides key items) get refreshed. This also includes the coupons. Using this method, it's possible to cycle the location of the coupon spawn. This doesn't add an extra one to your count, so doing this is mostly useless. Just make sure to always grab a coupon if you die or reload, to be safe.
  
• One will always spawn inside the asylum, and one will always spawn when you escape the asylum.

Once you've collected your 10 coupons, load up a new game and enter the kitchen. On one of the tables will be a box with fried chicken inside of it. Interact with the chicken and the achievement will unlock.

Credit to Realwild for confirming this info.

#1) In the 1F Staff Locker Room. It's inside the middle locker to the right of the sign that reads "16".











#2) In the 1F Ward A Doctor's Office. It will be on the desk in front of the stethoscope.











#3) Next to the TV in the room directly next to the 1F Doctor's Office.











#4) Behind the trash can in the last stall of the Ward A Men's Bathroom.











#5) In the Basement 1st Altar room. It will be under the bench with the note on it.











#6) In the 2F Chapel Library. It's in the middle row, where the leaning white and blue books are.











#7) In the 2F Library Filing Room. It will be on the left-most shelf with the yellow books.
WARNING: This one is literally impossible to see. You will need to walk up to the shelf and check if your reticle turns red.











#8) In the 2F Pharmacy Lost and Found section. On a box directly below the comb spawn point.











#9) In the large, northern bedroom on the 2nd floor. There's a spawn point for the mirror in this room.

These can only be found after leaving the asylum, but before entering the underground bunker.

#10) From the door you use to enter the asylum, go down the right side to spot a few large dumpsters. The coupon will be on one of the wooden pallets.











#11) Facing the dumpsters from the previous location, look to your left to spot an awning, a statue, and a gazebo. The coupon will be under the awning, directly in front of the 2nd to last metal support beam.












#12) In the small hut, between the wall and the lockers.











#13) In the same small hut, on the right corner of the metal table.











#14) In the same small hut, under the right-most wooden chair.