I couldn't say how long it will be available for, I have also seen some on H.com. It seems that more seasonal colors are popping up on the website lately that I would not have expected to see. Maybe when you see someone report the purchase you can ask them what letter stamp it is, then we can guess how long the color may be available for. At first I thought it was just old stock, but now it seems to be remaining available even in very desirable bags which would not sit around unsold for a season or more.
@Meta may have this info or perhaps could refer you to a thread with the info, she is a treasure trove of Hermes data.