Do Entei, Raikou, and Suicune appear anywhere?

I have caught Entei and Suicune, but Raikou is eluding me. Is there a set of places like Cresselia, or just bad RNG?

it can be anywhere but I think you have a better chance of finding it if you have a pokemon with the ability volt absorb at the front of your party

Oh, thanks

Xd just caught it lol