Vaniville town:
Fletchling at your own house
Rhyhorn in front of our house
Route 4:
Marill in the maze
Route 11 and 5:
Two Lucarios (with Korrina), disappear after interaction with Korrina
Camphrier town:
Fletchling in the Hotel
Espurr in a house
Parfum Palace:
Furfrou in the maze (disappears after completing an event)
Marill on the second floor
Route 7:
Snorlax on bridge (disappears after battle)
Litleo, Marill and 2 Espurrs in the Day Care
Ambrette town:
Furfrou and Espurr in Hotel
Espurr in Aquarium
Route 9:
Rhyhorn at the beginning (rideable)
Cyllage city:
Furfrou in the Hotel
Marill in a house
Espurr in another house
Geosenge town:
Furfrou in Hotel
Shalour city:
Espurr in a house
Lucario with Korrina (top floor)
Lucario in the tower of mastery (2nd floor)
Coumarine city:
Espurr in a house
Furfrou in another house
Route 12:
Skiddos in the ranch (mostly rideable)
Laverre city:
Fletchling in a house
Furfrou, Litleo, Fletchling and Espurr in Pokemon fan club
Dendemille town:
Litleo in a house
Frost Cavern:
Abomasnow in the deepest part
Route 17:
Mamoswine right in the beginning (rideable)
Snowbelle city:
Abomasnow all over the city
Litleo in a house
Kiloude city:
Litleo in a house
Espurr in Battle Maison
Team Flare HQ:
Yveltal in the core of the building (Pokemon Y)
Xerneas in the core of the building (Pokemon X)
Terminus cave:
Zygarde at the heart of the cave
Pokemon Village:
One Espurr, one Snorlax and two Furfrous spread out in the field
Mewtwo in the cave
Lumiose city:
Gogoats near every Gogat Shuttle (rideable)
South Boulevard:
Furfrou walking around
Some sleeping Skiddos in a building
Two sleeping Skiddo outside
An Espurr in a different building
Two Fletchling in a different building
North Boulevard:
Marill on the field
Lucario and Diggersby in Cafe Battaille
Two sleeping Skiddos outside
Litleo in a building
Litleo on the field
Espurr in Lumiose Museum
Espurr on the field
Mamoswine in a building
Two Fletchling in Cafe Triste
Fletchling on third floor of Hotel Richissime
Marill on fourth floor of Hotel Richissime
Furfrou on fifth floor of Hotel Richissime
Centrico Plaza:
Two Diggersby on the field
One Pumpkaboo (hard to spot) which goes "Ka ka ka!" when you interact with it.
Estival Avenue:
Pumpkaboo and Diggersby in the Lumiose Press
Lucario in Cafe Rouleau
Vernal Avenue:
Furfrou in Cafe Woof
Two Furfrous in Friseur Furfrou
Espurr in Herboriste (the herb shop)
Fletchling in Cafe Classe
Furfrou in Cafe Cyclone (Vert Plaza)
Hibernal Avenue:
Fletchling in Restaurant Le Wow
Two Marills, one Furfrou and one Espurr in Cafe Kizuna
Fletchling in Sushi High Roller (Rouge plaza)
Espurr (Mimi) in Looker Bureau (Rouge plaza)
Autumnal Avenue:
Fletchling on field
Espurr in Juice Shoppe
Espurr in Pokeball Boutique
One Marill, Espurr and Pumpkaboo in Cafe Pokemon Amie
Passageways:
Between Couriway town and Route 19: Furfrou
Between Lumiose city and Route 13: Furfrou
Between Lumiose and Route 16: Espurr
I may have passed a lot of things under my radar though, so leave a comment if you think anything is missing.
Source: My 3DS, I scrutinised the whole of Kalos to get this result, the comment section as well.
Hope I helped!
