Yeah GS is only available in Japan you might need to check with reliable Japanese dealers like Seiya-san
www.seiyajapan.com or Higuchi-san
www.higuchi-inc.com. after checking for some GS models using the internet i saw this 72 Hour Automatic Grand Seiko it's stunning and Limited to 200 models only.
Grand Seiko Automatic SBGL003
i also saw this Grand Seiko Spring Drive Divers
and also this complicated GS model the SBGC004
also the SBGC003 in action!
http://www.youtube.com/watch?v=4s2_gjSy8yU
more here
http://www.seiko-watch.co.jp/gs/lineup/