Add Police vehicles at all car dealers to be purchased with money. just like unique vehicles for donators. And you can only use it from /v when you are playing as a cop. Why do this? I like to modify my police cars with nitro and neons. When i do this on current police cars that are on current server system, they cant be locked and can be stolen by any policeman, and some are reset to normal when u leave them behind.
So, if you buy them as personal vehicles, u can /pv or /rpv at anytime u want. i repeat, u can only call them when u play as cop.