By a strange and extremely mysterious coincidence I found a invite for sale on biddingpond. (
https://www.biddingpond.com/item.php?id=735)
The bidding starts at 0.01. (And I guess) It's just an experiment to see if people are willing to pay a small amount of btc for an invite.
Anyway, I will get more invites very soon which I'm perhaps willing to give away.