have any of you seen the movie The Book of Eli? having a sword there was totally believable, not to mention awesome, yet the guy with "power" and his lackeys had guns.
maybe a limited number of people control the remaining ammo. also, it could be that some monsters are impervious to bullets. maybe you'll get a magic shield that is impervious to bullets later on. gotta agree with Zelda having a manly face. ,aybe it's the hair.
all that being said, if i wanted to play something like a post-apocalyptic Zelda, I would play Crystalis for the NES.
Eli didn't have a sword, he had a machete. It's probably easier to find a machete than a sword.
If a monster can be hit by an arrow or a sword, what reasonable explanation is there that they'd be impervious to bullets?
I don't expect ammo and guns to be lying around left and right but it wouldn't be unreasonable to find a gun in the post apocalypse and have some ammo.