Klaus-Adler,
You might have to hit up ebay to find Paul Miraldi’s book because it has been a while since it was published, but it is definitely worth the search. He is on FB in various Vietnam Uniform and Gear type sites. You might be able to get a copy straight from him. The Grunt book from Andrea Press is still available at some model shops.
Something that I wish the reference books would cover better is the methods of how equipment is attached to the belt. I think that would be helpful for modelers and some of the manufacturers. Too often I low hanging ammo pouches on figures most likely because a modeler may not know how they should be.
In regards to collecting uniforms and gear in the UK, there is a collector in the UK named Jack Ewing who has a pretty extensive collection who sells items from time to time. Most of his proces are pretty decent. He is on FB and he is also a member of a pretty good reenactment group.
I hope this will be helpful.
