I had the Shiny Charm from completing the National Dex and this still took me forever.
Still doesn't make me feel better, espcecially since I know all the gen 6 shiny mechanics.
Default rate around 1/4000 ish (screw exact numbers. I know the general and that's good enough)
With Shiny charm around 1/1000 ish
Hoard battle without around 1/1000. With, around 1/300
Chain-Fishing 1/? down to as little as 5 depending on how long your streak is (Shiny charm makes it faster)
In Friend Safari and via Dex Nav 1/500 ish (shiny charm no effect)
In Mirage Spot around 1/200o ish without shiny charm, about 1/500 ish with
Poke-Radar 1/? down to 1/4-6 after a long enough chain. (shiny charm has no effect)
But none of that's helped me. That's why I'm going back and doing a catch/evolve -a-thon. To get a shiny charm and maybe help me get my first shiny in years.