Trev, you're going in October correct? If so, begin training in boots now.
Many people will say that it isn't necessary. They're right, it isn't. It will, however, be advantageous. Many people will say that training in boots will only lead to injury. They're wrong, it won't. The key is being smart about your training. Ease your way into running in them. DO NOT go out and run 5 miles the first day you get them. Start by running 1 mile in them once a week. After about 3 or 4 weeks, make it two miles. After another 3 or 4 weeks, make it three miles. For OCS, three miles will be good to go. Also, I would highly recommend going for a hike (30-50 lb. pack; in boots and utes) every 10 or 15 days. Training in boots now will allow your body to adapt gradually, thus avoiding injury. Furthermore, it will show you where your feet tend to develop blisters and you can figure out how to avoid them.
As far as what type of boots and where to purchase them, try
http://www.quanticoboot.com Go ahead and get one of the official USMC pairs. I recommend either the Belleville jungles or the Bates Lites. For more information regarding boots check out
http://www.marineocs.com and search for "boots." Boots have been discussed numerous times and in incredible detail.
Finally, while we're on the topic, I would recommend getting several good pair of boot socks. Thorlo and Fox River both make a "combat" boot sock that is very good. Black is good to go. Any further questions about boots or OCS in general let me know.