Funnily enough when I was in Harrods one time early in my quest for a Herbag and when I asked if they had one they did but it was in Lime. I didn't like the colour but as I was sitting taking a look at it I could see another customer being shown a Herbag in brown or another dark colour. When I indicated to the SA those people he told me that they had ordered that bag and were there to pick it up. Now I wonder how that is possible when I've been told that you can't order bags you want and they don't know when they get deliveries or what items will be in those deliveries and you just have to check back by coming into store as they can't/won't contact you.
I would definitely be up for having some kind of subgroup for those stalking Herbags in London.
I asked my NBS SA to transfer a Herbag from the collection at the time from another store (maybe even Selfridges where I was told display only) and he did that and I collected 2-3 weeks later. I wasn't a major client then (CDC and a wallet).
I know this is not the UK store but I could share (or even ask myself) my Warsaw SA - they had a few rare Herbags recently (the black one shown above with gold and also black coated canvas). It might be worth flying there to pick it up (cheap flights are from eg. Luton). Please let me know.