Basically there are two standard places to play, Spielbank Hamburg
www.spielbank-hamburg.de, Esplanade) or Casino Schenefeld (
www.casino-sh.de).
Esplanada has 2/4 Cash Games on most evenings, its best to call them before and reserve a seat. Haven't been in Schenefeld for a while, but they used to play 2,5/5. There are no smaller games in the casino.
You can also go to Lübeck Travemünde. It's about 150km away but easy accessible by train. 2/4 NL game also but it's cheaper and more fishy (hamburg can be pretty tough, especially cause many players treat the game like it was a 5/10 regarding bets/raises)
hope that helps,
cheers