For future Orr researchers who come across this thread, the Missouri Historical Review article can be found in the January 1966 issue (Vol. 40, No. 2). It's at pp. 127-148 and is entitled "Nobody's Nominee: Sample Orr and the Election of 1860" by B.B. Lightfoot. It's well-researched, and does a very good job in providing a profile of the man.