Somebody knows if I can buy "yerba mate" somewhere in Poland???
Basically any shop in the larger cities that sells tea, spices or international specialty foods will have it. It's easy to find, there is a very large selection, and it's not at all that expensive. In Wrocław, there are easily ten places just in the old town where you can buy it, including the tea stand in Hala Targowa, and at least one shop in each of the shopping centers.