You're right: everything on tap is better and you're not likely to find a dunkel served that way in the states. There's a great German pub in Seattle called Altstadt Bierhalle & Brathaus. They get kegs shipped from Germany and serve a decent selection of German brews on tap. Even in that case, there's always a larger selection of weisbeirs than dunkels; the lighter brews just seem more popular in Germany, I suppose.