There are million of specialized stores in this AKIHABARA area alone,
Akiba is short name of this Akihabara, originally called AKIBA-ga-HARA.
I bought a 120->100V transformer at this shop in order to install "washlet"
in our home in Toronto, because today's "washlet" is computer controlled.
We also bought the second "washlet" in Tokyo, which uses 100 volt.
Although you do not worry about voltage difference too much today.