Looking for digital version of School Books

I’m looking for digital version of school books, (PDF, Doc, . . . ) format, in any English-speaking countries.

Grade 3, 4 and 5. And, second year of high school.

Any websites?

I contacted some schools in England and US but they didn’t hear of it.

Not all the books, any books of these: Science, history, art, social science.

I just want to take a look and study the context and text complexity of the mentioned school books.

I suggest trying this site:
http://en.wikibooks.org/wiki/Main_Page