Once you have actived the mod in your game or NMM, you will find the items in the workshop menu under:

Decorations -> Misc
Decorations -> Wall Mounted -> Flags

Material requirements:

Wall Flag - 5 cloth.
Flag on pole - 5 cloth, 2 steel.
Flag on pole (animated) - 5 cloth, 2 steel.
Flag on stand - 5 cloth, 2 wood.