I'd contact the HKCAD for info first. As far as I know level 6 (native speakers) only need an Authorised Examiner (those check pilots who test Instrument Ratings and Aircraft Ratings) to sign them off. If you are below ("undetermined"), then you'd need a language expert. Back then they had to forward your voice recordings to somebody in Australia to get this done.
This info is quite old, but it came via mailing through HKAC from Peter Moores (who is one of the few who underwent a training course for Level 6 assessment together with Bob Tandy).
Another route is asking these guys:
Aviation English Language Solution
1203 Harcourt House
39 Gloucester Road, Wanchai
HK (SAR), China
Tel: +852 2528 9321
Fax: +852 2520 0329