Theres a Smuggler in NC in Pepper Park 3, next to some PSI-Smugglers, he sells Apartments in Outzone and Pepper Park.

Another Smuggler in the Dome in Abandoned Sector 4 sells Appartments in Random Locations and Appartments in Sector 1, 2, 3, 7 and 8.

Apartments in the Canyon are available from the Twilight Guardian-FSM (Faction Supply Manager) afaik (as far as i know).