Flags + Insignia clothing

ebonartgallery

Items with multiple national flag insignia - armbands, arm patches that go over existing clothing, hats, belt/belt buckles, 

MoonCraft3D

tabards!

wynn3000

good idea

andreretogasser

Why not shaders?

A bit like: https://www.daz3d.com/iray-super-shaders-patriotic-patterns-merchant-resource    ; .....but with more national colors....