I'm pretty sure that HP doesn't have any Reverb stock, nor have ever had any. Probably still waiting for the first batch. They delayed the launch from April 26th to May 8th and then just decided to list the headset so that its "officially launched" but immediately set as "Out of stock", trying to make it look like they sold out in minutes. But, no one anywhere on the internet has said they are able to get any kind of ship date. If they sold out in minutes from HP, Amazon, and Best Buy, someone on one of the discussion groups would have said they snagged one. HP is trying to pull a bit of a fast one.
...which would be fine if they just came out and said, "hey all, sorry, first shipments have been delayed 3 weeks, and we are working diligently to get them shipped. Will continue to update, etc..."
Instead, they are having all the websites just say" Hey, they are really popular and sold out quickly! Don't know when we will get more!" That is a complete lie.