This is awesome. You probably have enough stuff already, but there's a whole bunch of books from the 19th and early 20th century on Archive.org that might be useful for your lessons.

I went on a downloading spree a few years ago when I thought they were going to take the Internet away from us and I have about 250gb of ebooks saved. I know a lot of people turn their noses up at ebooks, but nigga its free knowledge.