Japan is one of the most attractive markets in Asia for its strong purchasing power of consumers. Culture-wise, Japan is known for its "closed society" due to the geographical isolation from other countries.
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.