It definitely takes a large amount of concentration and mental awareness to properly OC. Your primary tool for proper weapons retention is your state of mind. I would never OC if I was the type to walk around Condition White. While most BG's may be amateur (relatively), I wouldn't take the risk of a SERPA as my primary defense from being disarmed and taking one in the back.
As far as training...
Depending on your background, I would start with Frontsight. They cover weapons retention in the Empty Hand defense and Advance Tactical Handgun courses.
If you've had some training andcan find an availability, I would train withSuerez Internationalon this.