triton,
IMO, I wouldn't buy the turtle. I can't speak for the laws in China, but in the U.S., it is the posession that gets you in trouble, not your intentions. The reason is that so many people who get caught with illegal wildlife say: 1) I didn't know it was illegal. 2) I knew it was illegal, and I was just about to turn it in 3) I'm holding it for a friend(grin).
I know of one case where a person had picked up a sea turtle in Florida, kept it in an aquarium, learned it was illegal, contacted the USFWS and was promptly arrested. This may sound harsh, but in reality, he kept the turtle for a year and only "discovered" it was illegal when it began to outgrow his tank. USFWS did the smart thing by arresting this guy, even though at face value it looked like they were being bullies.
I can validate what Ocean Park HK told you - they cannot accept the animal as a donation. They are accredited by the Association of Zoos and Aquariums, and they have to abide by their regulations - one of which is to only acquire animals through legal/ethical channels. Accepting a CITES 1 animal from the public isn't ethical for them, and may be illegal.
Jay