Fly to the resort area once the NAtional pokedex has been unlocked. Then give the desired pokemon the EXP. Share. Battle with high pokemon as the pokemon are lvl 50+. You can get some rare pokemon like Oddish, Gloom, Pinsir and if you head north yoou can encounter Beldum and Cacturne etc. Good luck. I use this all the time to raise my eggs and evolve the
pokemon!