From Amazon
edding 4090 Chalk Marker - White - 1 Chalk Pen - Chisel Tip 4-15 mm - Broad-Tipped Wet Wipe Pen for Chalkboards, Windows, Glass, Mirrors - Liquid Chalk Marker Pens for Opaque Coverage
Conrad Electronic
Edding Kreidemarker 4090 4-4090049 Industrial marker White 4 mm, 15 mm