The BSCO are about as mysterious as freaking unicorns. And I know, Rockstar may have been too lazy to add them, or they didn't have enough time, but what about your reasoning? Do they even exist? Did you replace them? Post your reasons why, if you do have some.
I, for one, have worked out my reasoning - for my GTA V game set in 1995, the BCSO were almost fully dissolved after the LSCS took over patrol operations - the only remnant of the force being their yet-to-be replaced 1992 Caprice 9C1s, and even then, Los Santos officers are the ones who drive them.
I know, many of you may not have a reason, but it'd be interesting to know. Even if it's on the fly, or you don't even care about the BCSO.