Or try Abe:
http://www.abebooks.co.uk/Type in something like "school atlas" as your title and put in a year as a keyword.
Some of the 1930s ones are quite expensive, but there is a 1940 Webster for only £2.95 at the moment.
The bonus of using an atlas is that you get lots of maps.
Early school atlases are usually quite clear, and the 1950s Phillips ones usually include pictures and essays about trade etc.
You might also consider a book of timetables - I have a reprint of Bradshaw's railway timetables for Call of Cthulhu games. The 1920s ones include adverts for hotels etc, and steamship timetables.
If you are looking at a UK setting, Bradshaw's are invaluable. I noticed that "The Works" had a repro 1890s version last week. Not sure if there is something similar for other countries? Perhaps Baedeker?