Walk over to Tokyu Hands (which is in the Takashima Times Square development right by Shinjuku Station) and take a look at the kitchen floor there. They carry a wide range of knives - from cheapo up to professional grade.

If you don't find what you're looking for there, then you might want to make a trip to a knife-specialist like this one in Tsukiji:
http://www.nenohi.co.jp/tukiji/index.html

Tsukiji is a pretty good bet for any kind of culinary equipment because of all the restaurateurs who go there daily for their supplies.

I dont know a knife specialist in the area of the Park Hyatt, but I expect there is one in Shinjuku... maybe the concierge can hunt one down for you.

BTW - Is your friend accustomed to working with a Japanese knife? The blade is constructed quite differently from those of Western cooking knives.

BTW2 - I've come across this tradition in England and in Japan... when giving a knife, you make sure that the recipient gives you a penny in return. I think this must be because of some idea that a knife could "cut" the friendship, so it's better to make a transaction rather than a gift of a knife... Has anyone else come across this?