I have big feet in Japan

If you live close to a big city you might be able to find some western shoe or clothing stores that sell your size of shoes. I know that in Tokyo you can always try stores like Adidas, Zara or H&M. Furthermore, you might want to check out this article from the Japan Times, they have a whole article dedicated to bigger sized shoes.

http://www.japantimes.co.jp/community/2013/06/04/how-tos/hunting-for-big-foot-large-shoes-tough-to-track-down-in-tokyo/#.WYpxGBiiHaY

The last option I can give is to order your shoes online from a store that ships to Japan.

Good luck!

There's one shop called JELLYBEANS. 

It is very recommended by many foreigners living in Japan and you can find in in a variety of malls accross Japan. IThey have suitable shoes for big feet and normal foreigner sized feet. I recommend you take a look.
I know you can find jellybeans in some lalaport malls and maybe online as well.

Hi Julie!
This is the Jellybean shoe shop in tokyo they mentioned above:
http://www.jelly-beansshop.com/shop/pages/shoplist.aspx

This page above shows you the locations of the jellybean shops in Tokyo and around. The page is in Japanese so please use google translator if you don't understand (click somewhere on the page and choose "translate this page". You can buysoes online through that site as well.