First you must go with waterfall op to the waterfall, then you must go in to the cave. Take the stair on your right hand. Take highest (in your screen, the stair that is the most above) stair. Go down over the jump, and try to stay on the left side. There you will find another stair, go in. Surf to the cave in the north, go in the cave, surf to the other side, there you will find Bagon. It is a little bit hard to find, but believe me that is the only spot where you can find them.