It isn't available, and not coming any time soon from Mazda, and due to the low volume of Mazda sales combined with the complexity of the headunit's relationship with the rest of the car's system I doubt we will see anything from the aftermarket for a while. To replace the radio we need to have firmware from iDatalink Maestro, or Metra for their aftermarket adaptors that can control the CanBUS for things like the automatic wipers, the lights, door lock controls and the myriad of other settings the radio handles. This is available for high volume car brands like GM, BMW, or Toyota but not so much for us at Mazda.
The only saving grace is that besides some body panel stuff, it's nearly the same radio (and the same software based on previous software updates all being the same file regardless of car) across the entire Mazda range. Hopefully that will be enough to motivate iDatalink to help us. Without them we will never see any harnesses show up to give us aftermaket radios.