Sorry it took me a while, hope this is helpful. The bibliography from my old Marian Reforms paper follows. Especially useful were Gabba, Kildahl, Smith. If you want my full paper (with page numbers for references) let me know, I'll find a place to put up the pdf or you can PM me with an email address. Cheers.

Adcock, F. E. The Roman Art of War Under the Republic. New York: Barnes and Noble Books, 1995.

Cicero. De Republica. In The Political Works of Marcus Tullius Cicero: Comprising his Treatise on the Commonwealth; and his Treatise on the Laws Vol I. Translated by Francis Barham. London: Edmund Spettigue, 1841-42.

Dobson, M. The Army of the Roman Republic: The Second Century BC, Polybius and the Camps at Numantia, Spain. Oxford: Oxbow Books, 2008.

Gabba, E. Republican Rome, the Army, and the Allies. Berkeley: University of California Press, 1976.

Goldsworthy, A. The Roman Army at War 100 BC-AD 200. Oxford: Clarendon Press, 1996.

Kildahl, P. Caius Marius. New York: Twayne Publishers, 1968.

Livy. Ab Urbe Conditi Libri. Translated by F. G. Moore. Cambridge: Harvard University Press, 1949.

Plutarch. Gaius Marius. In Fall of the Roman Republic. Translated by Rex Warner. London: Penguin Books, 2005.

Plutarch. Tiberius Gracchus. In Makers of Rome. Translated by Ian Scott-Kilvert. London: Penguin Books, 1965.

Sallust. The Jugurthine War. Translated by John Selby Watson. New York and London: Harper & Brothers, 1899.

Scullard, H. From the Gracchi to Nero: a History of Rome 133 BC to AD 68. London: Routledge, 1982.

Seyffert, O. Dictionary of Classical Antiquities. Edited by H. Nettleship and J. E. Sandys, http://www.ancientlibrary.com/seyffert/index.html.

Smith, R. Service in the Post-Marian Army. Manchester: Manchester University Press, 1958.