well you could go out an buy a $1200 paintball marker that is the latest and greatest, but i get the feeling that's not what you're looking for.
I suggest looking into the tippman A5 with the e-trigger. I do not recommend this to a paintball player because it's long, bulky and has a strange, impractical hopper for playing paintball with. However, it's one of the few markers that allow the user to look down barrel sights which is what law enforcement will be used to. Secondly it requires little no no mantience and it includes a hopper with the marker, meaning what you buy is what you need, excluding a co2 tank of course. They do use a single 9v battery that needs replaced on occasion and every few thousand shots they reccomend that you drop some paintball oil in where you screw in the tank and fire 50 or so shots to make sure everything stayed lubed up.
here's a link to the tippman A5
here's a link to a fairly new marker that supposedly uses the same guts as the A5, meaning it should be equal in quality.
With either marker I suggest the use of co2 as it's cheaper, easier to find and give you more shots than a high pressure air tank would.(I'm pretty sure the fire station will have the ability to fill them)
The problem will come where they hopper is only a 200 round capacity. you can upgrade them with
this 400 round hopper, but that's the biggest one that I can find. If you need more paint you can always buy a cheap vest or pod pack from any paintball place and use it to hold extra 150 round pods of paint on your body.