We had them on grand auctions a few times, and I think some people got them from mystery boxes (again from grand auctions) as well. Senticore got one from winning pet wars too. Other than these, I think it is not possible to get one ingame, yet.
The materials to craft those potions are not that hard to gather (blood moss, fire ruby from gold panning and a druid reagant from killing the druids in ilshenar). I am pretty sure you can find someone to make them for you, if you gather all the materials.
