While you're exploring Sliph Co, there should be one that the president is holding it. defeat Givoanni and then talk to the president he'll give you a master ball. This is the only Master Ball that is obtainable in the game without using cheats.
Cheating in video games
Pokémon Trading Card Game
Cheating in video games involves a video game player using non-standard methods for creating an advantage beyond normal gameplay, usually to make the game easier. Cheats sometimes may take the form of "secrets" placed by game developers themselves.
Cheats may be activated from within the game itself (a cheat code implemented by the original game developers); or created by third-party software (a game trainer) or hardware (a cheat cartridge). They can also be realised by exploiting software bugs.
The Pokémon Trading Card Game (ポケモンカードゲーム Pokemon Kādo Gēmu, "Pokemon Card Game"), abbreviated as PCG or Pokémon TCG is a collectible card game, based on the Pokemon video game series, first published in October 1996 by Media Factory in Japan. In the US, it was initially published by Wizards of the Coast, the company that produces Magic: The Gathering, in December 1998. Nintendo eventually took over publishing the video games in June 2003.
It is one of Nintendo's last remaining strong links to its heritage as a playing card company.
Games for Windows was a brand owned by Microsoft and introduced in 2006 to coincide with the release of Windows Vista and Windows 7. The brand represents a standardized technical certification program and online service for Windows games, bringing a measure of regulation to the PC game market in much the same way that console manufacturers regulate their platforms. The branding program is open to both first-party and third-party publishers.
Games for Windows was promoted through convention kiosks and through other forums as early as 2005. The promotional push culminated in a deal with Ziff Davis Media to rename the Computer Gaming World magazine to Games for Windows: The Official Magazine. The first GFW issue was published for November 2006, and the magazine was defunct as of 2008.