Please correct me if I'm wrong, but I believe that the normal ("closed") DS9 uniforms have been removed from the Tailor in conjunction with the new Featured Episode series. They now must be unlocked by a reward from the Cardassian Lock Boxes.
The open-jacket variant is part of the Open Jackets costume pack, and was unaffected by this change.
I could be wrong (again), but I don't recall buying the original DS9 uniforms, just the open variant. I think they were always free.
I don't use the DS9 uniforms myself, but I bought the DS9 unlock on the Exchange for cheap just to (re)complete my collection of uniforms.