The shields of the mod "Spartan Shields" didn't show the skin that i'm using
This image is with a normal shield of minecraft

And this one is with the Diamond Shield from the mod

What version of the game?
Have you tried added them to the support list?
https://github.com/RiskyKen/Armourers-Workshop/wiki/%5BGuide%5D-Skinning-Modded-Items