Although this hat is rarely sold, I still think you need more than one sale; If I'm not mistaken, the '1 sale rule' applies to hats that are rarely sold because of the number of people capable of buying them; for example, the Burning Crone's Dome price (http://backpack.tf/vote/id/527b030f4cd7b894078b4568) was accepted because only one exists, and there are very few people that are capable/willing to buy it.

TL;DR: I think you need two sales, somebody please tell me if I'm wrong.