How do আপনি get a Red Chain?

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

"A mythical chain that is ব্যক্ত to link the legendary পোকেমন that created the Sinnoh region.
It is ব্যক্ত 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 দ্বারা using an action replay অথবা 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