I was just casually browsing the forums, and noticed your post.

If your family was here during the 40's and lived on the West coast the National Archives may have records to help you sort out your paternal grandmother's maiden name. I found records with names of great grandparents, and other relations living in Japan, on records from the war relocation authority [WRA] which documented the governments removal of Japanese American's, and their Issei parents to concentrations camps. Each individual will have a record with family number. Also, check for immigration records. They have a new way of doing that these day's. Just do an internet search for uscis genealogy...