A zillion years ago I ran into this issue myself. Through 2nd grade we were only allowed to check out books in the "little kids" section of the school library, then we could move to the other end of the stacks in 3rd grade. By the beginning of 2nd grade I kept sneaking over to the big kids section. I don't know if my mom got involved, but I remember that I ended up with a deal with the librarian that I could check out books from that section, but I had to go in during recess to do it (not when the other kids were there so they would not wnat to do it, too). Worked out okay...
And, of course, you can always provide the books yourself via your public library or purchasing them. D lugged a full 3-volume copy of Lord of the Rings around all through 2nd grade as she read it. She took it in every day, read it during class reading time while her classmates were working their way through more typical 2nd grade fare.
