Yes, as you say, it is rather easy to get hold of goods from "strange" countries with even more "strange" languages.
Google is a great help.
I am sure, you will be happy with the two Polish books, good buys at a reasonable price, lots of pictures. And the one book in English.
You will have to wait 2-3 weeks until the books from Poland and the goods from Siberia reach you.
Nothing to do about that.
It is long way from the Chinese border to somewhere in Europe.
But the posts from Russia and Poland are reliable, so much I have learned.
Then you has to translate the Polish text, but again Google helps, even if it is not very good at Polish, especially when the Polish writer has a little special way of expressing himself. But with the text in the book about the Poznanians, the translation via Google goes rather well. And with a dictionary and when you has learned a few of the Polish military uniform terms, it goes rather easy.
Good luck with an interesting subject.