How do آپ get a Red Chain?

آپ can't outside of hacking. It was meant to be held سے طرف کی the player before Cyrus used it, as it has a description.

"A mythical chain that is کہا to link the legendary Pokémon that created the Sinnoh region.
It is کہا that the Red Chain summons Dialga and Palkia when it is put together."

However, this idea was later scrapped but the data left in.

yeah to obtain the red chain the only option is hacking simpily سے طرف کی using an action replay یا even better owning an R4 as my dear friend has im not much of a hacker myself but to obtain such wicked items i had to resolve to it hope this helped