Below are a couple of doctors who can perform the Hong Kong Seafarers Medical that can be used to get a RYA/MCA Commercial Endorsement. The cost is approximately HKD600 and lasts for 2 years if under 55 years old, 1 year if older than 55 years.
Dr Nicolson & Associates
402B New World Tower, 16-18 Queens Road Central, Central, Hong Kong
For more information on the Hong Kong medical see here: https://www.elegislation.gov.hk/hk/cap478O
For details on the medical check see here: https://www.ilo.org/sector/Resources/codes-of-practice-and-guidelines/WCMS_174794/lang–en/index.htm