Thanks for the link.
My Japanese is not that good yet so it's difficult for me to find appropriate sites in Japanese.
I contacted a few of the companies listed on that site (waiting for answer at the moment). But I think it's not the kind of traders I am looking for.
I am particularly looking for wholesale companies which sell products from the Japanese company HouseFoods. HouseFoods is making food products as well as some prescription-free products.
Thanks for any further help.