To catch Pokémon in Pokémon Let’s Go you’re going to need a large supply of Poké Balls. If you run out you won’t be able to catch any more, so you want to keep many in reserve. The easiest and fastest way to get Poké Balls in Pokémon Let’s Go is by purchasing them, but there are other ways to get them if you don’t have any money to buy them.
When you do have extra cash, you’re going to want to stock up. They cost 100 Poké Dollars a piece and can be found at the Poké Mart. This store is found in various towns and is a blue building with a Poké Ball logo on the top of it.
Other ways to get Poké Balls is to find them in the world. Different items will be hidden in the world and some of them contain different things. Alongside Poké Balls, these items will contain other consumables that you can use in the game.
There are also some NPC characters in Pokémon Let’s Go that will give you Poké Balls for free. In the Mount Moon and Digletts Cave you’ll find a character that will give you free Poké Balls when you talk with them.
Trying to rely on finding them or going to this character each time you need Poké Balls isn’t the way to go. The best thing to do is when you are in a town, is to stock up on Poké Balls at the Poké Mart. If you don’t have any cash you can sell other items that you’ve collected and increase your supply of PokéBalls so that you never run out.