From Scratchpad

Although this quest is filed under Shinagawa, everything you need to do is in Shinjuku.

Talk to the female Messian that is by the exit to Shinuya. Select the second option to ask about the road to Arcadia. If your alignment is close enough to Law, you will get the Shinagawa map data for free. Otherwise, you will have to pay either five thousand or ten thousand makka.