This is an untold story!
More of a non-story, actually. The surrounding parishes have their own local governments and police departments - the NOPD lacks jurisdiction there.
I could give detailed description of what happened where and when, but the following map and link show the way the area was affected.
As far as why unconstitutional firearm seizures did not occur in other parishes damaged by Katrina (especially St. Bernard, which was flooded worst of all), the red and blue electoral map tells the tale. I don't have a link to that handy, but Orleans is blue - the surrounding parishes very red indeed.
Why, it's almost as though right-minded people got the hell out of that urban hellhole and relocated to the area surrounding the city, huh? Imagine that. ;^)