Here's your list of starter sources:

• May, James A. Trials of Character: The Eloquence of Ciceronian Ethos. Chapel Hill: U of North Carolina P, 1988.
• Dugan, John. Making a New Man: Ciceronian Self-Fashioning in the Rhetorical Works. New York: Oxford UP, 2005.
• Enos, Richard Leo. Speaking of Cicero ...and his Mother: A Research Note on an Ancient Greek Inscription and the Study of Classical Rhetoric. Rhetoric Review 24.4: 457-465.
• Meador, Prentice A, Jr. "Rhetoric and Humanism in Cicero." Journal of Philosophy and Rhetoric 3.1: 1-12.
• Smith, Robert E. III. "Rhetoric as Social Act: Cicero and the Technical Writing Model." Journal of Technical Writing and Communication. 22.4: 337-356.
• Ochs, Donovan J. "Cicero and Philosophic Inventio." Rhetoric Society Quarterly. 19.3: 217-227.