Hello! This is a great question, different that others. I'm surprised others haven't responded to you yet.
My knowledge is limited with imports/exports but I will try to be of value matching my experience and insights elsewhere to fit your needs.
My name is Humberto Valle, I'm the founder of a small agency in Texas & Arizona www.Unthink.me - we bring big business marketing tools and experts to small startup companies.

I am assuming you are a merchant with access to retailers/buyers in Japan then? This is what my strategy would be if I was in your shoes then.
Option A) Travel to the origin destination, in this case European countries and personally network with such companies. I had a fellow from Indonesia a few years back that did just that in an effort to find a local distributor who could help with logistics and sales for their metal sculptures (the ones you find on PF Changs...)
Option B) What I could try doing would be leverage competing or similar website/companies who import/export products you may have in mind and find what paid ads and keywords they are using to show up on Google Ads for certain searches and if you have a website, even try to implement those searches on your own site so that these European companies can find you as well that way.
1) through paid ads, after finding potential companies and their exact ads
2) through seo and lead generation promoting directly to them through SEO and social sites like Linkedin.

There is so much advises and so much answers from different different persons like i am the one of them if u want to find the companies who export there goods to japan as my opinion u have to find the companies first who actually sells goods of japanies companies so u may find the way from that companies after taking with them or meeting with that companies they help you much better then us they tell you the name of companies who exports the goods to japan and why japan takes goods from that companies what was the reasons which makes japan more intreseting to buys their goods from that companies why they should not make their good own self may be it helps you to clear your other things also