Since their removal as a random event, regular shades appear in the Stronghold of Security and the Catacombs of Kourend. If you plan on doing Shades for your Slayer task, it is recommended to slay them outside of Mort'ton. As those are combat level 40. You can also slay regular shades on the fourth level of the Stronghold. There is a Safespot in the room when you enter, behind the skeleton at the northernmost point. However, these are a lot harder to slay, and are combat level 159.