Loco Chantelle is a Named Enemy in DLC1 of Borderlands 3. You encounter this “Mayor’s Killer Look” in the VIP Tower on The Handsome Jackpot. They are located in the High Roller Lounge area.
You can farm Loco Chantelle for the Nukem as it is the dedicated loot source for this item. Loco Chantelle’s legendary item has a 10% drop chance.