This Poké Ball can be obtained as a reward for filling the Pokédex and catching 340 Pokémon. You will be able to find this item in the Pokédex app rewards menu by pressing the X button.
You can get Moon Ball from the auctions in the market area in Porto Marinada. The key is to make the highest bid to get the item.
Auctions in Porto Marinada are unlocked after completing Cascarrafa's Gym Challenge, and the featured items will change every day, in-game and in real-time, but can be manually repositioned by closing the game and moving up the date of your auction console one day.
You can get Moon Ball as a reward for completing the Academy Ace Tournament. This is unlocked after beating the game and eliminating all 8 Gym Leaders.
This is all you need to know about how to get Moon Ball in Pokémon Scarlet Violet, so we hope we have been as helpful as possible, so you can get a lot out of this PokeBall.