If you want to have access to the "special" items of Chiaki goodness, then you need to join the Chiaki Kuriyama Shrine Forum and achieve the rank of "Goddess Disciple" and these items availability will be added unto you.

 These items are not open to the general public for obvious reasons.  The Shrine has these "Special" items that are virtually impossible to receive because of their age, availability, rarity and price but the Shrine is the clearinghouse for said items and you will not be disappointed.