You have to become the Champion and see have seen all 151 Pokemon in the Sinnoh Region Pokedex to get the Poke radar What you Need
-Poke Radar and the the poketch app 20 (the Poke Radar checker)
-A good shiny hunting team (pokemon with stats move and false swipe are good)
-Pokeballs (like quickballs and repeatball)
-Repels (Max is good)
How to get the Items
The Poke Radar you can get after seeing all of the sinnoh pokemon and going to Professor Rowan laboratory then talking him
You can the Poketch app 20 from Professor Oak in Pal Park after beating the game and getting the national dex
You can find Healing item, Pokeballs and, repel in Pokemarts
-DON'T run away you must catch or defeat the pokemon
-Always go to the same type of grass
-Grass patch must be 4 steps away from your characters position
How to Chain
Before we start you want to and register the Poke Radar and get all the items I showed before
Ok now let start!
First, find a big grass patch and save the game then use a repel then press Y. Some grass should be moving and you want to walk into one of those grass patchs. When you encounter a pokemon that you want you to chain catch or faint it. By catching it there is a 10% more chance of seeing that pokemon. After that keep on going for the same grass patch and follow the rules.
If you don't see a good grass patch you walk up down not running into the grass patchs and reset the poke radar.
The Chain might just randomly break for no reason
After a chain of 40 you want to keep reseting the Poke Radar until you find a shint patch. You have a 1/200 chance of a shiny patch appearing.
If your chain breaks reset the game and get your items back
-Getting on your bike
-turning off the game
-Encounting a random pokemon
-Running from battle