Here's a link to all the free themes and avatars. They will be leaving the store on mobile and the web so this is probably the easiest way to get it before
PSN Avatar Not Showing | David Artiss
L.A. Noire PS3 Avatars and Themes Now Available - iGrandTheftAuto
PSN avatars for Kingdom Hearts III Sora, Donald, and Goofy available to PlayStation Plus (Japan) members from January 18 - Kingdom Hearts News - KH13 · for Kingdom Hearts
Death Stranding Avatar Code Revealed; Gives Two PlayStation Avatars - Just Push Start
PS4 1.76 UI Mods: Custom PSN User Avatar & Alpha 0.11 by eXtreme | PSXHAX - PSXHACKS
How to Change Your Avatar on the PS4 - Guide | Push Square
New Persona 5 Character Themes and Avatars Released on Japanese PSN - Persona Central
PS4 Users Can Buy Avatars On The PSN Next Week | Attack of the Fanboy