This guide would require some way of playing edited ROMs (such as a flash cart, NDS emulator etc). This guide assumes you already know how to dump your own ROM legally, and how to play the edited ROMs. As such, this guide will not entertain such questions, as it is not the point of this guide. This method works for any language'd variant of Diamond, Pearl, Platinum, HeartGold, SoulSilver, Black, White, Black 2, and White 2.
Note: the shinies obtained via this guide will only appear shiny. When the save is viewed in PKHeX, and when shiny Pokémon (resultant of this modification) is transferred forward, chances are they will not be shiny. Additionally, this guide will not give you 100% shiny encounters.
However, the shiny odds for these fake/temporary shinies are still higher than base rate, and may interest people that do not intend to transfer forward nor trade to vanilla games.
Anyhow, we will not be providing any arm9.bin or modified ROMs, as linking to or providing data files extracted from ROMs are against our forum's rules.
However do not fear, as the steps regarding how to extract the arm9.bin from your own dump and then re-injecting them, are included in this guide.
The 3 easy steps:
1. Extracting the decompressed version of the arm9.bin
2. Performing the edit
3. Injecting the edited arm9.bin back into your game
Extracting the decompressed version of the arm9.bin
Performing the edit
Injecting the edited arm9.bin back into your game
Extra: Testing whether the modification works
FAQs and Explanations:
Sources (that I remember):
Bond697's original work to increase the shiny xor threshold on Pokemon Black 2
Me expanding on Bond697's work to find a working offset for Black/White
My explanation for why the shiny is fake/temporary
Bulbapedia's page on Shiny Pokémon