The spezi in the Biergarten is not actual brand name Spezi or even something like Mezzo Mix (which used to be at Club Cool). It’s just a mixture of Coca-Cola and Fanta Orange. They’ll gladly make it for you at Sommerfest (the counter right next to the Biergarten) but you could also go to any local self serve soda fountain such as McDonald’s or a gas station and mix it up yourself. Coca-Cola Orange from a Coca-Cola Freestyle machine would also be somewhat similar.