It's the culture where a lot of people don't donate when they die as they won't be able to enter the after life is the body is not complete.
It's common in HK and China.
Also if you were able to find a donor legally you'd be well down the list unless you have $$$$ to jump the queue or find a body to harvest in a back street deal.
Organ donation of a commercial nature is illegal in Hk. You can donate your organ while alive or dead, but if payment is involved then it's illegal.
Organ donation in China often involves human harvesting. If you haven't hear about this I suggest watching this movie or doing a Google search. Probably better off for him to get a kidney transplant close to home and not risk some of the added complications one might find in HK or China. People can live for a long time on dialysis. In some cases depending on your needs you can even qualify for home hemodialysis while you sleep. Human Harvest
Doubt the prisoners would be consenting, being executed to provide the organs sounds pretty lacking in consent to me.
China carrying out over 60,000 illegal organ transplants annually, report finds | The Independent
only brain stem death person can be suitably donated organs. Even in China still have more patients to wait for organ transplantation for survival.