I can't speak for non U.S. military, but our military regulations specifically state that we are NOT to wear individual cmponents of our uniforms as part of civilian clothing. But, as has been pointed out, no one is going to get arrested for it. However, amongst vets it absolutely would be noticed. As with everything, most won't bother to say anything and would likely commemt as a conversation starter (myself included). However, there are others...

As to an Army kilt with a pin made to represent the units, I would think tjat is fine. f you are having.the pin made, then it is not a piece of the uniform. I think that would be a great idea.