Look for the green arrow on the maps. (Name of the closest NPC on the map.)
Find Regent's Square Cat - Near entrance of Scotland (diagonal from Sir Reginald Baxby)
Find Hyde Park Cat - By the south entrance of the gazebo near the Greenhouse (Mr. Rowley)
Find Digmoore Station Cat - from the entrance, just past the left wall. (Sherlock Bones)
Find Big Ben Cat - from the entrance of the 12th floor, behind the first crates on the left.
The 12th floor is right after the floor with the silver chests.