Here is a WIP theme for XMB made from “Yoshi’s TV Game Icons” collection by a Japanese author (1st folder top-left for games icons).
Icons used for current version:
-from Yoshi-kun website:
The focus is on Japanese systems (Famicom instead of NES and so on). I try to complete it by drawing some new ones.
To have something mostly complete you could:
-Copy and rename RetroArch\assets\xmb\monochrome folder to RetroArch\assets\xmb\custom
-Drop the theme icons in RetroArch\assets\xmb\custom\png folder and replace the old ones.
-In settings>User Interface>menu>menu icon theme select “custom” and restart Retroarch.
Original icons resized to 256x256 are included so that you can use something you’d prefer (NES, SMS…).