ID Card 48: In your first visit to the Sewers, follow the path to the Town Hall until you find a room with 2 cell-like short tunnels on the left side. The ID Card is in the first one, on an open grey suitcase.
ID Card 49: In your path from the Town Hall to the Supermarket. It's on a toolbox up a ladder, in the first big room.
ID Card 50: In the Town Hall after the attack. It's on a notice board next to a workbench, near the door to the sewers where you entered the Town Hall the first time.