Are you getting mad that you can't find a securicar? Here is how you find them. (See Below)
1.)Do Joey's mission were you ram into the side of one. If you do that one all you have to do is get the securicar take it to grage, put it in it then, blow it up so the mission is failed and then you can take it to the docks.
2.)Do missions for Donald Love on the 2nd island then once you get to the ones with the securiars during thoes missions you see them a lot more then get one fail the mission and take it to the docks.
3.)Get the Barracks OL on the 2nd island take a cruise and after a while you will bump into one.
4.Do cop or firefighter missions on any island and you may find one after a few times.
5.)Get all 6 stars lit up and you will find them.
6.)Cruise around the 2nd or 3rd island for a long time and might find one.
7.)Rarely see them when not trying to look for one.