How to find an (Undergrad) research assistant position in europe?
The Dutch term you are looking for is Studentassistent. 

My experience in the Netherlands (some time ago and in the social sciences) is that these positions are fairly rare. Moreover they were rarely advertised. If someone had funding for such a position, a student was directly asked. At my current institution in Germany we have so much funding earmarked for "HiWis" we have trouble filling all the positions. 

So I don't think it is a European thing; there are huge differences between countries and disciplines.