Here's my save for the Car Fanatic trophy (found all vehicles):
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There are 94/95 cars found. The last vehicle is the International Police Wagon. Start Cases/Arson/Free Roam and find the Bus Stop Shooting side mission off the corner of Beverly & Union. Getting to the vehicle is tricky as approaching from the wrong angle will trigger the mission, and you won't be able to get the car. Come up to the barricade from the south on Union, and you'll see two police wagons. Go slowly forward and veer right to the sidewalk. Look left and when you're staring straight in line at the nearest wagon, that's the correct angle.