It's the nightmare of every Pokemon Go player. You finally find that rare Pokemon in a remote part of town, only to discover you're out of PokeBalls. PokeBalls are the secret lifeblood of Pokemon Go and if you're serious about "catching them all", you'd better make sure you have a full stock of PokeBalls at all time.
Collecting PokeBalls is a simple process in Pokemon Go. You can either retrieve them from PokeStops, get them while leveling up, or purchase them from the Pokemon Go store. Once you reach higher levels, you'll also begin to get Great Balls and Ultra Balls from PokeStops, although you'll want to reserve those for harder to catch Pokemon. If you don't want to waste PokeBalls on hard to catch Pokemon (the ones with red or yellow "catch circles), be sure to feed them a Razz Berry first as it makes catching them much easier.
Although players start off with what seems like a limitless supply of PokeBalls, there will come a time in the game that you begin to run low, especially if you're catching Pokemon in an area without a lot of PokeStops. However, areas with a concentrated number of PokeStops are the best way to quickly build your PokeBall reserves back up. If you can find an area with four or five PokeStops and visit each one in a five minute loop, you can get dozens of PokeBalls (and lots of XP) in a relatively short amount of time. Remember that if your bag is full, you won't be able to grab items at PokeStops. so be sure to toss out any unnecessary Potions or Revives that you don't need before going on a PokeBall run.
One weird rumor that has sprung up among fans is that players can retrieve thrown PokeBalls by tapping them when they missed. While there are plenty of unpublicized tricks in Pokemon Go, retrieving missing PokeBalls isn't one of them.
Pokemon Go is available in the United States, Australia and New Zealand.