As I've been playing with collage more in my mailart, I've been looking for snips of old text that correspond with the theme of a piece. Working in a library as I do, I have access to discarded books, but it's often tricky to get exactly what I'm looking for.
Recently I began fooling around with Google Books, and I'm falling in love with it as a source for old texts. I can do a keyword search and limit to "Full View" in the sidebar. Anything I then find can be "snipped out" using the "Clip" tool. I open the resulting URL in another tab or window, and voila! I have a .jpg or .png image of just the rectangle I've selected. If I limit by time period, I can get some great old stuff.
This works for images, too, but they can be harder to track down, since Google Books works by searching text.
When I have what I want, I print it out on some vintage paper I've scrounged, and once it's pasted into the collage, it looks like I tore it from a book myself!
Give it a try.