If a group of us trained together and became proficient at patrolling and the like, even if we didn't live close to one another, you now have 4 or 5 guys that can teach others in their own town or neighborhood.
As far as where to find like minded individuals.....
If the SHTF really bad your local Volunteer Firehouse is where they will be. Those guys will be the ones running things.
Local Police will more than likely leave to protect their own families. Most of them do not live where they work. They will go home. They will not travel 15 miles to patrol your town.
The mayor of your town will more than likely put these Volunteer Firefighters in charge and the local Sheriff will more than likely Deputize them.
If you are young enough, join the Volunteer Fire Department. If you aren't, after a SHTF event, make yourself known to them. Tell them your abilities and hang around and help out.
They can put you to work manning a checkpoint or used as a messenger for communication.
Those Firefighters and the Town Mayor will be the law.
They live in the same town. The town is their home.
This is not set in stone with rules written down anywhere but it's the only logical conclusion if society collapses. Those fireman be the only able bodied uniformed men that live within walking distance of the town.
If gas is no longer an option, the world gets smaller.
As far as firearms go, if the SHTF hard enough that there are no cops around, those that have firearms will carry them no matter who they are.
If thats whats left in charge after a collapse might as well make my claim for Town Mayor now.