Yes just under 5 million population, however you are making the assumption that everyone is on the list. Good attempt

There are a mere 300,000 people diagnosed/ suffering kidney problems annually helped by The National Kidney Foundation of Singapore who take care of 2/3 of Singapore's kidney patient population. Therefore, 450 000 require assistance, dialysis or a kidney. Specifics I do not know.
However, you now suggest that all prisoners sentanced to death to not be allowed to donate!!!? That completely goes against a Utilitarianist, ethic of care and non-consequential viewpoints to say a few, where in general supports the viewpoint of the 'greater good for the greatest number'.
And
ethic of care is
completely supporting your moral basis viewpoint, but in regards to everyone who could
possibly receive a kidney or other organ is denied the right by a LAW in which you suggest (in question)!