When items are new releases, like these are, they will eventually be on a cycle. The cycle could be 6 months or could be one year it depends on when our Gm and Admin think the item box are ready to be sold again. They could also be sold at special times of years. Example: Near our anniversary in August or during the holiday season in Dec/Jan.
I suspect that like the "Custom blood set" these items will be more for special occasions like the anniversary or the Winter Holidays. However, it never hurts to ask.