This should help you:
You can actually get them immediately after beating the elite four. When you visit the town elder in Celestic Town, she will show you a book. Then you find the Adamant Orb and Lustrous Orb in Mt.Coronet. Then, go inside to the cave inside Celestic Town. Cynthia will be inside. Talk to her. Respond yes to everything. Then go to where you first entered the Distortion World in Spear Pillar and Dialga will be in a blue portal to the left. Palkia will be in a pink portal to the right. They are both at lv.70.
Watch that video to see how.