I'm glad you asked because the way to get a Salemence, which I have myself, is to evolve a Bagon to a Shelgon, then finally into a Salemence.
u capture a bagon in the sparcly gold like cave were team magma was. you surf up water fall and go up to the highest extent. then u r able to get bagon, evolve into shelgon then to salamance about at lv. 50 or 60