No corroborated info on your query, I’m afraid. I think the essential word in use is “headquarters”, as opposed to a focal or meeting place while the Allied military forces were on the road or otherwise in a fluid situation. Various hotels across Java did serve as temporary or long-term headquarters for certain echelons during the Java campaign (certainly the major hotel in Tjilatjap so served, but for how long a period I have no idea). On the other end of the spectrum, Blackburn and William-Powlett could merely have met for a civilized lunch—alone or with another two or three officers—while they discussed the particulars of attaching B Squadron, 3rd Hussars, to Blackforce. Not much help, am I?
The last I heard, some of the records of the squadron that managed to come back from the Far East were being held in the Queen's Own Hussars Regimental Museum, Lord Leycester Hospital building, Warwick. Of course, the 3rd The King's Own Hussars became part of the QOH by amalgamation 59 years ago. If you’re located anywhere but in the UK, you may wish to attempt to find a researcher nearby who knows the turf and may be able to ferret out the info you seek.