Pokemon GO has a new event going on which increases the chance of getting water types Pokemon. In addition to that, shiny Pokemon have also made their way into the game.
Right now the only shiny Pokemon in the game are Magikarp and Gyarados, as a shiny Magikarp can evolve into a shiny version of Gyarados. Because Gyarados is harder to find, your best bet will be to find a shiny Magikarp in the wild and evolve it whenever you get the chance.
Sadly, finding a wild shiny Magikarp is actually a bit harder than it sounds since you can’t tell from the map if it’s a special one or not. If you try looking for one with a Lure Module, your odds might go up slightly, but the shiny factor is as random as the CP is when you encounter Pokemon. This means while your friend might have a shiny Pokemon on their screen, it might not be shiny for you, and the Pokemon’s CP will likely be different too.
You’ll want to make full use of the current water event that is going on and make use of plenty of Lure Modules too. Other than that, all you can do is hope as shiny Pokemon are notorious for being hard to find in the original games, and that trend will probably continue in Pokemon GO.