Treeko is only available before the event of weddirring island, as for the septileite I'm not sure if it's in this locations but, if you have surf, strenght (maybe rock smash) go to apocillips Cave and find a temple at the north of the cave, then go up and you should find a exit, If I'm not wrong, the septileite should be on the floor
Guys, 1 question, anyone knows where to find a Sun stone in the game, I'm currently in Kepler city (Arietta's town) and I have not found one until here, and I would like to evolve my petilil into Liligant before I go further in the story.