Just got my first shiny ever (a Bulbasaur) through breeding on the second egg. That made me get hyped for some shiny hunting, and now I really want a shiny Gigalith. I've been trying to breed it via MM, but this Poké Radar thing caught my attention. I never used it before, and I want to know if there is any grass patch where I can chain for Roggenrolas in Y (I heard that you can find Pokémon that you couldn't normally if you use the radar). Google didn't yield any results, so sorry if I'm asking for spoon feeding.

tl;dr: Can I chain for shiny Roggenrolas in Y using the Poké Radar? Where?

Thanks in advance!