The articles do not offer much in the way of evidences. This is understandable since the authoritarian nature of China makes it hard to gather any evidence in the first place. I remain skeptical over the fact that Uighurs (Caucasians) and ethnic Chinese (East Asians) are genetically different and the recipient's body is very likely to reject the organ.

organs may not necessarily be taken for transplantation only, tissues from various parts of human body are valuable for lab research of various kinds.

Also, what kind of evidence would be sufficient for you? A video footage of harvesting from one of the camps?