The Old Market Sector existed on the planet of Coruscant. In the time of the Galactic Empire's reign, the Mon Calamari species were "relocated" after riots occurred in this area. A droid mechanic, a neighbor to the human child Anandra Milon, remembered that Anandra received her initial speeder after the Old Market Sector riots.
Alexander Freed penned the short story "One Thousand Levels Down," which first mentioned the Old Market Sector, and it was released in Star Wars Insider 151 during 2014.