This is a very difficult question. I am not familiar with Mikado Pearl of Ginza, and I do not believe one is in existence today. It is very possible this was a small pearl shop that went out of business years ago.
I did a few searches, found nothing in any of the comprehensive pearl books I have on hand, but there are a few tidbits I can share with you that may help you out in your search.
First:
There is really no record of 'Mikado Pearl' on Google - at least none that helps you.
I then used Google.co.jp, the Japanese Google search engine and did a search for: 真珠 帝, which if your computer can read Kanji, means pearl Mikado. You can find the result here:
http://www.google.com/search?hl=en&lr=&q=+真珠+帝
I scanned several and only found one reference that listed a company name in partnership with a design which won second place at a Kobe Pearl show. I searched the company and found they do not deal in pearls directly. So this tells me that the company does not currently exist.
There is a Jewelry company in Dubai that goes by the name:
Mikado Intl Jewellers L.L.C.
You may want to contact them and see if they are at all related to Mikado of Japan: +971-4-3527480, fax +971-4-3527817.
There is another company that registered the name 'MIKADO CULTURED PEARL JEWELRY' in 1994. But the name was abandoned in 1996. This is the only address I found on file for them.
JewelMak Inc. CORPORATION NEW YORK 7 West 45th Street New York NEW YORK 10036
The word Mikado is an old Japanese word for Emperor - but specifically 'Emperor of Japan' - that is not used much today. But because it is a famous old word, unfortunately it is used in many company names today.
Sorry I could not have been of more help. I hope this information can lead you in the right direction.
