The DS TV-tuner is only available in Japan (it will only work there on the 1seg network), and when Nintendo of Japan opened their pre-order here the other day (you can only buy it online from the Nintendo JP web shop), the server crashed.
You can also pre-order the WanSeg TV Tuner DS from Play-Asia.com. But remember, this TV-tuner will only work in Japan. It will be released on November 23.
Here’s a video of the TV-tuner in action (source: GameBrink.com):