When I installed PLEX and started assigning posters I came across these, and loved them.  Typically for PLEX though, not all of them were there.  I had seasons 1, 2, 3 and 5, but not 4.  I managed to find them all on the net though.  They come from DVD covers and look so good that  have them for my Merlin posters.  Unfortunately there is only limited material for the complete series graphics, and has labels over it.

https://www.google.com/search?tbs=simg:CAQSgAEafgsQsIynCBpiCmAIAxIo5hbnFukW7BaDBKcR3xa3F-UWpw7UPcYk0z32N5YntC3SPbItxyS8NBowNizZH4fIrAvEcS1hF0C7N_1_1h-gq4AD5pavuxbJnA_1A4q0etUSj27CYVGqvLKxPImIAQMCxCOrv4IGgoKCAgBEgQclvdkDA,isz:m&sxsrf=ALiCzsbgrkVyll4oWnO-9-IU5O6wLVgpHg:1664057892821&q=merlin&tbm=isch&sa=X&ved=2ahUKEwjN_djcuq76AhW73jgGHUJZDTQQ2A4oAXoECAEQOw&biw=1920&bih=955&dpr=2 (External Link)

I don't have the software or skills to remove the labels and restore the bottom corners so I just cropped it.  if anyone does have the software and skill, please feel free to add it.