Supposedly if you loot one of those (or the 2 Hill Horror) Masks this month, they will be added to your account as permanent items - Some people claim you just need one in your inventory, others say you need to loot it, so best to err on the safe side and loot one to be sure: There have been reports of people selling them in-game for 1-2 million aUEC, but they seem reasonably common and there's no guarantee you'll get a permanent one from these.
I found and grabbed several of the Hill Horror ones (both reasonably common) Sunday night, then was lucky on Monday night and found 2 Vanduul ones (at the same location), so grabbed one, and let others in the server know there was one available, then waited at the box for the player to arrive and "loot" it\remove it from the box (to prevent possible box despawn if no players nearby after it had been opened). Last night I spent a few hours with Execute trying to find the new Hill Horror mask, but only found a Vanduul one for him.
To find them, look in the red boxes at mining or research outposts on planets and moons (they don't appear in boxes at bunkers or places like "Bountiful Harvest" from what I have observed and heard - I plan to try the abandoned outposts tonight to test)... Please at least "open" white boxes there even though they won't have the masks (grab a cruz for hydration, perhaps), as this will hopefully trigger the box' reset timer, notifying the server it is OK to remove it after x time and spawn a new box at the location (hopefully red) as a replacement - Many sites last night had a lot of white boxes but no red ones (or the model for the red box showed it had been "opened" by another player, while the white box models appeared untouched).