The plastic cam buckles are available at REI stores.
http://www.itwnexus.com/cam-buckles.html
I wear my bags on my right shoulder,and am in the process of modding the strap on my Timbuk2 with one of these:
http://www.itwnexus.com/catalog/inde...b5a54fdc86ffc0
I'm going to cut the strap somewhere in the middle and add the buckle in-line with a D ring laced into the lower end. This will allow the strap to function much like the one on my Baileyworks Pro.