According to the official Hong Kong China visa office in Wanchai they close to the public and outsource! business:
http://www.fmcoprc.gov.hk{:target="_blank"}
From now on the official visa place is http://www.visaforchina.org{:target="_blank"} landing site, or http://bio.visaforchina.org/HKG2_EN{:target="_blank"} for Hong Kong.
Another option are travel agents, here is one that is also used by many to buy China visas:
http://www.fbt-chinavisa.com.hk/services.html{:target="_blank"}