Want to obtain Chinese car registration for my Hong Kong based car.

The dual plates are applied for and subsequently issued by the PRC authorities in Guangzhou. The approval is based on your investment in Guangdong province. Nowadays they are extremely difficult to secure. The company I use to work for invested in Shenzhen in 1985 and we secured a dual plate permit based on our investment into a JV with a chinese partner connected to the Shenzhen Special Economic Zone Development Co, essentially the #1 government company in Shenzhen. To my knowledge up until I left the JV 1994-2005, I was the only foreigner who had cross border driving status of a non-commercial vehicle as all other users of the dual plates were either HK investors or PRC government officials or SOE's with clout/connections. A company such as Hutchison Whampoa, the developer at Yantian Port, for all their clout only had dual plates for commercial vehicles, ie buses to ferry staff across, nothing in the non commercial class ie sedans, for managers. That is how hard they are to secure. An Aussie mate of mine recently got his approval through, based on his investment in Zhuhai. His was for a sedan.
Hope this is of some assistance.