After I got back my stuff, I tried to record some stuff. It's pretty diverse, with some interesting audio events like bakery sellers "chanting" to attract the client in the subway, strange recorded voices and music in a supermarket, a subway employee with a megaphone shouting informations... Plus some street noises etc.
http://punishyourself.free.fr/fieldrecordingsjapan/september22 : .wav
http://punishyourself.free.fr/fieldrecordingsjapan/september22/september22.rar : mp3 archive
PS : finding the Lost and Found office in a Tokyo subway station can be more difficult than finding where you left your bag, really.