Unless you live in Japan and can order directly from Obitsu's online store, you're going to see some mark up on Obitsu dolls and parts. One of the largest Obitsu retailers in the US is the Junky Spot.
http://www.junkyspot.com/Their policy is that if it appears on their website, it's in stock. Unfortunately they do not stock many Obitsu body parts, but they will order them for you.
If you can't wait and have to have it nooooow, the fastest, best place to get Obitsu parts is going to Parabox.
http://parabox.jp/eng_new/Parabox stocks just about everything for Obitsus as well as some of their own Parabox designed, Obitsu manufactured dolls and parts, such as the 40cm and 45cm bodies.