Happy Holidays!
All the direct sellers of carbon products that I know of are in mainland China. Not sure if there is much in Hong Kong. You could try doing some internet searches or contact some of the direct sellers and see if they know of anyone in Hong Kong selling their products.
Hmm.. I'm interested in whether or not you can just walk into a shop or some type of market and purchase them directly while you're in China, as well. Would be pretty cool if you could, and we def want pics if so!