Go to the Cycling Road between Eterna and Oreburgh City. Use cut on the trees next to the entrance to the Cycling Road. Head right to the back of the route where you will see the cave to Wayward cave. Instead of entering the cave, go under the bridge and keeping trying to head up, moving across each time. You will notice a path and continue upwards. You will enter a cave that requires Flash. Don't bother with Flash and simply head left. If you're playing D/P then you need Strength (It is not needed in Platinum). In that room you can find Gible. There is a 20% chance of finding it though.
If you want TM Earthquake as well, continue along the cycling ramps into the final room.