It's available on Amazon.de,
here's a link
http://www.amazon.de/Das-Boot-Die-Fe...?ie=UTF8&s=dvd
It's only 15 Euros, quite a good price. I myself only know the standard movie and the director's cut versions, so I will probably buy that double-dvd 5 hours set myself. For those who never saw that movie, it's a MUST!