What are the chances of that happening?

[Darien Shields]

What exactly are the chances of any given pokemon being Shiny, and in particular, Groudon/Kyogre. Also, is there any easy way to capture them without Master Balls? I have one, but I want to hold it back for a Lati, and preferably a shiny Lati at that (I have a lot of patience ^_^)

Thanks all.