“And though many have guns even though NYC has absurdly strict rules, they are mostly glocks and other hand guns.
Not much during a battle.”
In such a scenario you use the handgun to acquire a rifle from wherever you can. Police stations, the few gun shops, whatever.
Can’t get into the police station?
Steal a D-9 and doze your way in.
Once you have the rifle you use both to acquire ammunition for both.
Once suitably armed you go on the offensive.
Note there is a steep and dangerous learning curve in all this. There are probably more trained veterans in your area than you know. They’ll pop up when the situation calls for them.
Stunned silence..
Where the heck did you learn all that??