This paper, written for the British International Studies Association's Annual Conference, discusses arming of private security contractors and the issues involved in adhering to international regulations (ITAR, etc.). Also discussed is the 'paradox' involved in quelling the illigitimate flow of arms to troubled regions, while allowing the PMCs to do their jobs.
Full text can be found here.
The DDTC also offers a fairly decent discussion on approval of arms tranactions for PMCs here.
