The Cartels Event was made permanent on the 07.24.2021.
It can always be activated in the Main Menu.
Any of the six underbosses can spawn at 4 set locations in the Villa Ultraviolet.
2 spawn during the fight with Joey Ultraviolet.
Additionally, an underboss can spawn after you killed a neon-glowing Cartel Operative anywhere in the galaxy.
FISH SLAP!!!, Franco Firewall, Josie Byte, Roaster, The Tenderizer, Tyrone Smallums