I've heard that it can be quite difficult to buy western sized clothes in Japan. We're not looking to 'shop' but I would like to know where I can quickly buy some regular clothes if BA lose out luggage.

Carrying more than spare socks/underwear in our carry on is not an option.

So, is there a Gap, Levis, A&F, Marks and Spencer or whatever we can quickly head to if the worst happens?