"Nyah, nyah...I have it and you don't!"
How about "Unavailable"-- it's innocuous enough that it leaves it open for users to change their list if they choose to do so. e.g. I don't have Salvia 'Dancing Flame' available now - it's too hot to ship. But I certainly might in the fall or early next spring when I would change my list.
It would be interesting to know how sellers would like it shown - I think there's another thread about adding general comments under a user name on the individual's list to say that if a plant isn't available, write them.