You may already know the difficulties in potentially locating a laptop with an "English" keyboard in Japan, and if you don't, I recommend checking out HOW TO: Find a laptop with an English keyboard.
Reader Emelyn recently wrote in with four additional resources to find the somewhat elusive English keyboard in Japan (thanks Emelyn!):
Eisan Duty Free
Akihabara D.F.S. Tokyo-to, Chiyoda-ku, Soto Kanda
6-14-2 Sakai Suehiro Building, 2nd floor
Phone: 080-6687-1206 or 080-4067-1206
Look for Reiji (I believe he is Filipino, and he's fluent in Japanese and English)
Roppongi 5-5-8, B1F
Softbank phone: 080-3099-9190
Open 10am to 7pm, Monday to Saturday
AKKY International Duty-free Shop
They deliver merchandise right to your door.
370-0517 Gunma-ken, Oura Gun
Oizumi-machi, Nishikoizumi 3-1-23
If you know of other resources not included above, or in HOW TO: Find a laptop with an English keyboard, please let us know in the comments!