It can be found without the use of a cheat device. You can look here to see how.Yeah, normal encounter is finding them randomly. Bidoof, Starly, Bidoof, Starly, Bidoof, ooh shiny Starly.
RNG stands for Random Number Generator, something the game uses to set the IVs, natures and stuff of pokes you find, which poke will you find if you go to the grass, how many steps it takes to find a wild poke...
There is a way to abuse the RNG to force the game to give you pokes with flawless IVs and stuff. And this is what they mean by RNGing.
If you're interested in finding a shiny this way, you must know a certain number within your game, and you can only find that by finding a shiny the normal way, then sending it over to a hacker, so that the hacker examines the poke and tells you the secret number.