The outfit consists of a worn top hat, dress shirt with vest, black slacks and sunglasses. The disguise is tolerated in some parts of the first floor but on all other floors it is considered trespassing.
The disguise is located in one of the far wings of the attic. To access the room you must go between two tall cabinets covered in sheets then enter the room with a statue in the middle. The disguise is at the base of the statue in the middle of the room.
The only way to get the disguise in any way is to actually pick it up from inside Palais de Walewska itself. It can be found in the top floor's attic, in the most north eastern room, which is the north east tower room. There is no ladder to enter the room from the ground below, compared to the opposite tower to the south. To get to the room you need to walk through the attic. As you walk east on the north side of the attic, past the corridor connecting the northern and southern part, you will notice a slightly hidden entrance where two walls are overlapping each other. Go in through this entrance and keep heading east until you reach the tower room. When you open the door you will see a statue in the middle, covered by a sheet. The Vampire Magician disguise spawn is lying on the ground on the other side of the statue, right next to the statue in the middle of the room.
The nearest starting location you can choose during mission planning is the Attic, requiring a Mission Mastery level of 14 for Paris. As you spawn, simply walk west, then turn north into the corridor, and then turn east towards the tower room. Be aware of the two guards right near where you spawn, and another two on each side of the corridor.
The Vampire Magician outfit appears in the following: