Skullline.de has a pretty impressive collection of backstock of neofolk shirts. They have deadstock copies of the festival Strength Through Joy played with Boyd Rice and Death in June, as well as a few original Sol Invictus designs. I'm pretty annoyed because my last order contained a Blood Axis shirt and it never arrived, and they have never once replied to my emails. Before that last order it took like 3 months to receive anything, but at least it came. Maybe you'd have better luck being located in Finland.