Assuming your ThinkPad is newer than T/X/R/A 4x models and uses 20V AC adapter.

Yodobashi has this Lenovo ThinkPad 65W AC adapter in stock at Akiba and Shinjuku west exit stores. They also have this Lenovo ThinkPad 90W AC adapter online but not in stock in stores. You need the latter one if your ThinkPad has discrete graphics.

Amazon.co.jp offers same day delivery on some items to the greater Tokyo metropolitan area. Might be the better option if you can meet the order cutoff time of 8AM for the Lenovo ThinkPad 90W AC adapter.

I would enlist the help of the concierge to help you locate the AC adapter.