Informational Mentor Text List (for every Grade CCSS). This would be good to combine with the Common Core ELA Appendix that provides a list of mentor texts representative of desired grade-level writing achievement/focus.
You can order a box of books from this site. They will range from toddler to young adult books. Each box contains approximately 55 lbs (give or take). You can also order more age/grade specific books, but it costs a bit more.