Sure, you could look at your in-game Pokedex to figure out what's located where...but not only do you have to encounter a Pokemon first to access them there, that method isn't as useful as having all the information in one picture.
Thankfully, Reddit user Bobdor is way ahead of us—check out this awesome map he created. Click 'expand,' then right click and choose 'open in a new tab' to see the whole thing:
With this, hopefully you can have an easier time catching all the available Pokemon in X & Y. Do note that in order to get all the Pokemon listed under Friend Safari, you need at least a handful of friends registered. Additionally, Bobdor notes the following about the map:
If a pokemon has the "horde" symbol next to it, it doesn't mean that it ONLY comes in hordes. It just means that it DOES come in hordes.
Also if a pokemon has any "fishing" symbol next to it. I just put the easiest method for capture instead of listing all. For example if you can catch something with a good and super rod, I just put good because you don't NEED the super rod.
Happy Pokemon collecting!
PS - PDF version you can download available here.
(Via r/Pokemon)