I looked up the 5-6 german growers I know of, and none of them are within less than 2-3 hour drive from where you are staying.
I tried to find gardens, put it's hard since I don't speak a word of german! I'm sure that the local tourist office can help you out. You should have gone to the Netherlands if you want to see spring gardens. The giant Keukenhof tulip-daffodil garden is probably starting to bloom now.
Have a safe trip and a great time!
__________________ Camille
Completely orchid obsessed and loving every minute of it....