There is a very good, if rather small, hat shop just down the road from Hardbrücke station - go past the salvation army, heading towards the Viadukt . . in fact it is almost next door to the Freitag tower.
I`m quite sure you will find what you want there.
I often stop and look in the window - not becasue I want a hat - rahter becauuse they are all very distinctive.
However If I did want a hat - I may well buy it from there . . shall I shut up now?