Well, still no answer to the above. But had a recent email:
Hi. im competing in the action asia race on dec 10 and im coming from the philippines. we plan to rent bikes in HK for the race. i was wondering if you could recommend a bike shop that rents out mountain bikes for a day. thanks!
Charles Frew replied:
Try the Friendly Bike Shop on Lantau/Mui Wo..who also sponsor some of the Action Asia Series. Their link is on the AA website.