Where can I find books published before 1940 and before 1970?

Question

Books

The question, of course, is not for an IT resource, although it is related to searching for information on the Internet.
I am looking for textbooks, digitized, the history of Russia (RI) edition of 1936-1944 and edition in the 1970s. Of particular interest are the descriptions of the 17th-18th century.
I just don’t even know where to dig and where to look, and are there any copies or adaptations of the books of the above years? There is a suspicion that there are no digitized versions of them.

Answer 1

look at the book tracker. Specifically this:
booktracker.org/viewforum.php?f=1103
booktracker.org/viewforum.php?f=1076