Does anyone know where all the police are on this level, and how many there are? I've accounted for a good dozen or so and roamed the entire map, but I can't seen to find the final few.

Any suggestions?

As the missin intelligence says, you need a more systematic approach. When I was playing through it, I found a few at the edge areas of the map - south, northeast and north, IIRC.
Having a Scanner might be helpful here.

You probably solved this already but anyway, I remembering having to play this one twice because the last cop didn't show up at first. Second time I went through it in a clockwise motion and shot down the police car along the way, so that might have something to do with it.