If you want to nolife this yourself, you'll need three 3DS region systems and compatible games: NTSC-J (Japan), NTSC-U (North America, some Asia, some Africa), and PAL (Europe, Australia, some Asia, some Africa). C (China), K (South Korea), and T (Hong Kong, Taiwan) don't have any exclusives.
- J is the sole receiver of Elegant, but you can also use it for Continental, Monsoon, and Tundra.
- U is the only way to get Modern and Savanna.
- E nets you access to Garden, Meadow, and River. It's also the only way to snag Monsoon and Tundra if you don't have J, C, K, or T.
- Anything not mentioned can be picked up with either U or E. The only exceptions are Poke Ball and Fancy, which are of course event-exclusives.
For specific regions to set your 3DS to, read
https://www.pocketmonsters.net/content/Vivillon_Location_List