For english speaking customers, I will have to say Himeya will be your best bet...not sure if KGNE is back in stock or not, but it's been fluctuating for a while now.
http://shop.himeya.com
For ones who can speak/read Japanese, Getchu is your ultimate stop. They have the DVD version in stock usually and I think they might still have the CD version...
http://www.getchu.com