Where to buy contact lenses?

I am staying in Tokyo on vacations and lost my contact lens. Need to buy new one. Where can I do that? I would like to buy lenses for one day use only. Are these availble here. Are they expensive?

I suppose you are talking about products like One-day Acuvue? Those are quite popular, readily available at "contact lens shop," which actually has some affiliation with an eye doctor located (normally) next door or anyway quite close (or they may be combined). You first go talk to the contact lens shop, tell them what you want, then they will send you to the eye doctor next door for a simple check-up, who will write a prescription and you buy the lens back at the shop counter. If you are in big cities, ask at the hotel for contact lens shop.