Hook: Wall Large (Purple Rectangle)The Left-Mounted Monitor Display decoration fits into a large purple rectangle wall hook.
How to Get a Left-Mounted Monitor Display Decoration
Star Fortress Decorations
Star Fortresses are a type of solo or group content similar to flashpoints. You can not access Star Fortresses until you have completed Chapter 9 of Knights of the Fallen Empire (level 60+). The enemies in the Star Fortress have a chance of dropping bunch of different Star Fortress and Skytrooper Decorations, including the Left-Mounted Monitor Display decoration.
You can usually also find most Star Fortress decorations on the GTN, sold by other players who won them while doing a Star Fortress.