In Straits of Devastation, there's a small rock in the Sea of Elon, in the southeastern corner of the map, with a lone Quaggan NPC on it. Fight of a few risen and escort him back to shore in a short event chain, and he'll become a vendor, selling these for a brief period.
Black Lion chests drop this randomly.
Where can I buy this? xD
A little video on how to buy them :)
Wow, that is super detailed info! thanks for time you put into this man :)