Free: Contests & Raffles.
For the technological aspect of elk, North American Elk - Ecology and Management by DALE E. TOWEILL and JACK WARD THOMAS. For the "how to do it", I recommend Elknut's Playbook, DVD Series, and John Erikson's Tree Stand Hunting Rocky Mountain Elk. I find a lot of the other types of books are a lot of fluff with stories about taking their nephew out on their first hunt and this is what happened stories. That's all fine and dandy, but many of the bio type books are not really "how to do it" books... The books I mentioned will equip an elk hunter much better than some of the bio type books... just my thoughts
Hart Wixom has a fine book. Not Roosevelt specific, but he gives the subject more than just a casual paragraph or two. When I was guiding, this was what I fell back on when times got tough. He's old school and also relays a lot of info from the awesome Gaspar Puchi. That guy is the man.