Here are my percentages:
I allways search for eurobills from other countries in Emmen (near Germany) and with a popular Zoo visited by thousands of tourists...)
Also Groningen has been visited by the Giro dÍtalia and Assen had de TT (motorracing)...
I mostly buy a icecream or a tin of cola (with a 50 or 20 eurobill to get bills in return...

to get many banknotes in return of course..
1: Netherlands 47,5 %
2: Germany 20,3 %
3: Austria & France 6,2 % (both popular holiday destinations)
4: Belgium 6,1 %
5: Italy 6,0 %
6: Spain 3,9 %
7: Portugal / Greece 2,8 %
8: Ireland 2,3 % (visit the Irish pubs!!

)
9: Finland 0,8 %
My first Greek bill I received on the island Ameland, I had a real happy day there
I thougt bills from finland would never come to Holland, but last week I received 2 bills in a hamburgershop!!

If you don't like traveling, just watch where your Eurobill goes and let the banknote do the travelling for you!!