Alas, if you aren't in that community already you don't always know who these people are.
Tracking down good instructors in this day and age is actually quite simple. The internet provides some good information, which can be backstopped by something as simple as calling the local police department and asking who they train with and/or recommend. In fact, it's probably easier finding quality instructors in this field than in finding good martial arts instructors (the two are most certainly not always the same).
Here are two names that spring instantly to mind: Steve Tarani and Mas Ayoob. Any internet search will bring them up quickly, and their credentials and qualities can be verified by cross-checking other sources. I'd say Louis Awerbuck but he hasn't gotten around to teaching retention/disarms to the best of my knowledge.