It looks to be this place:
(有)ホワイトホルン
Tel 03-5816-4757
https://goo.gl/maps/C6CXkJAwfr53UeBZ6
〒110-0005 東京都台東区上野5-16-3
サスガ第3ビル4階
有限会社ホワイトホルン
Whitehorn Ltd
Sasuga No.3 Bldg
Ueno 5-16-3
Taito-ku Tokyo 110-0005
Watch manufacture, wholesale
No website, apparently, but because the Internet is amazing, here is a photo of their building directory.
View attachment 1407973
Click to expand...