Let's just say I think its very reasonable to email them and ask if they have any remaining stock. I'm personally referring to older ones, at least with my own experience.
Example. This past September there was a very limited time special, an Eid special I believe, where Kyara de Kalbar (amazing), Port Moresby (amazing), Oud Nuh (amazing) and Oud Royale 1985 (amazing and incredible value) were released. Now those were sold out long ago, now appropriately listed on my favorite hall of fame, Ensar Oud Legends (where I've spent countless hours reading and rereading). Now, some are really gone, or at least I assume. I have to believe it as I'm sure Ensar would have broke down and sold them just out of exhaustion with me pestering him so much.
Example 2. Early on I was looking to buy some of those very legends and happened upon a seller. Nobody here by the way. I reached out to the good Mr Coburn (who is a jewel by the way) who then connected me with Ensar (the maestro). It turns out I would have overpaid for most of the oils and there would have been no guarantee of their authenticity or that they were not adulterated. I got most of them, and others, from Ensar himself.
Now, I am not suggesting to not purchase from private sellers. I will sell some of mine someday (not Ensar/Taha/Adam though, fat chance of that), and I treat mine like treasures. I also have purchased some from private sellers. I have traded some. But I make sure I know who I'm dealing with. Like
@Oudamberlove, don't know him/her personally, but would do buy/trade without concern.
This is just my opinion, so please take it as that. Bottom line, it never hurts to ask Ensar, or any of the other guys if they have any left, even if no longer listed.