It looks to be very popular and even originating in Germany. Strange that it is so hard to find...
If you have a bread machine (or have a friend willing to share theirs)...you can make your own:
* 1 1/8 cups water
* 2 tablespoons molasses
* 1 tablespoon vegetable oil
* 1 teaspoon salt
* 2 cups all-purpose flour
* 1 1/2 cups rye flour
* 3 tablespoons packed brown sugar
* 1 tablespoon unsweetened cocoa powder
* 3/4 teaspoon caraway seed
* 2 teaspoons bread machine yeast
DIRECTIONS:
1. Place ingredients in the pan of the bread machine in the order recommended by the manufacturer.
2. Select the Basic cycle, and press Start.
Of course you will probably run into the same problem trying to locate half those ingredients here
Will keep an eye out for you though. I like that kind too.