The following are the Pokemon that come under the Fluctuating Experience Growth group:
Shroomish------->Breloom
Corphish-------->Crawdaunt
Drifloon--------->Drifblim
Gulpin--------->Swalot
Makuhita------->Hariyama
Wailmer-------->Wailord
Illumise
Seviper
All of these except Seviper can be obtained easily in-game. All these Pokemon require 1,640,000 experience points to reach Lv 100.