on map 11
Map 7.
on map 3
you find it on map land 8.
You'll Get it in the rock maps. In every rock map.
I just asked a friend and he told me that you can find one on map 7 or the one that is right under the entrance to the power plant.
after u get the national dex and catch dialga and palkia and the three lake Pokemon talk to oak in eterna and they apear on ur map
in the map 7
it is map 12
Map 11
Map 5
After you catch the main legendary (dialga, palkia, giratina) go to lake verity and mesprit will be in the cave in the middle of the lake. Talk to it and then it will flee and appear on your map app.
no
They are located all over the map.
in map 4
on map 1
map 8
in map 6,7,8,9,10,11,12