Who can help me to get in contact with a seller from mercary.jp

Hello,
I am looking for someone who has a Mercary.jp account and can help me to get in contact with a seller of a sold item. This seller has other items available to buy so it should be no problem to get in contact with him.
I am from Germany and can't register myself at mercary. In my case it is not a directly order for a proxy. Therefore my general proxy refuses to help in this case.