As unfortunate as that is this is not a universal problem, where I live 14/16/18/20 are readily available and competetive in price/TB, and they have been for a few years (at least the 14/16TB ones, not sure about 18/20). One would hope that the roll out of larger capacity drives would also result in more availability in your region - perhaps not of the largest capacity that exists, but at least of a larger capacity than is currently available to you.
Lucky you! I want to build a nice RAID array (currently my storage setup is ad hoc supporting about 14 TB), but I don't see why I should use 12 TB as a base when higher is available (outside my region).