But Carm's right, try the food section at Karstadt Mönckebergstraße, they have lots of "food from home"

Maybe you also ask at
Graeff's GetränkemarktAm Osdorfer Born 28
22549 Hamburg
Tel: 040-807 88 70
Fax: 040-80 78 87 17
Couldn't find it seaching for "root", but might be worth phoning them. They claim to be the "bester Getränkemarkt Deutschlands"...
It's also worth trying little Getränkemärkte round the cornder from where you live. There's a tiny one in Eimsbüttel, they say you should always ask if there's something you can't find, in most cases they can get it for you within two days. They even have Augustiner on stock *g*