FWIW regarding "it must be stainless."
Stainless steel resists rust but is softer than carbon steel. Match barrel makers love it because being softer it's easier to cut precisely. Both regular carbon and stainless can be black nitride treated. The cured coating is actually a lubricant and decreases friction and heat making the barrels last longer. But we probably don't use 'em enough for that to be a real world factor.
Hard chrome, chromium over a separate copper plating, is also used to prevent corrosion. Properly done chrome will outlast stainless, which is only corrosion resistant, not corrosion proof. Chrome is often used for high rate of fire barrels, as in full automatic weapon use. Hopefully, your neighborhood does not require that sort of rate of fire. Chrome linings also impart a small accuracy penalty that isn’t there with black nitride. Again not enough to be a real world consideration.
Just my $0.02 but IMHO black nitride is a better choice for general purpose use.
Jackie
PS
I also think that a revolver is a better choice for a survival kit. It can fire any ammo that will physically fit without feed or cycling issues even if you have to spin the cartridge and then physically eject a split case with the cleaning rod. But you have one of those

right. Plus the learning curve is short if some of the members of your party are not familiar with firearms.