I found some of my notes which might be of use.
The Meiji Gunshop is a short walk from Shinjukusanchome station. Follow the street signs towards the Koban (Police box) and the shop will be on the lefthand side of the road.
Meiji Gunshops' website is herehttp://www.shinjuku.or.jp/meijigun/
There is a map and the address in Japanese at the bottom of the page.
Hamada & Son website is herehttp://www.hamada-and-son.com/
If you ask at your hotel I'm sure they will help you find them.