Cabal Abbatoir Model unavailable for purchase in Galactic Exchange

In my quest towards being a true completionist and buying everything I'm left unable to unlock the Cabal Abbatoir Model. It's sitting there in my Other section, taunting me, taking me to the Galactic Exchange when I click it - but apart from a couple of Retrograde skins I've already bought everything there. Considering I've got five stars on all maps, including the DLC but not yet including challenge modes I assume it should have become available at some point in the past.