They've been in the game from the beginning, out of curiosity why are they suddenly the rage now? Felblades and Crystalline Swords are pretty obvious, for the same reason as Eternal Shields, but I don't see the draw to the Sephis Axe all of a sudden.
sephis axes drop in about 1-10 drops in the catacombs in pre seering. best way to farm them is with a smite monk and repeat over and over. when brought to post seering sephis axes can be expert salavaged for an steel ingot.
Its not a new stlye or something...I've been watching people search for these axes since I started. Its a rare skin weapon that happens to be of high demand. I myself was searching for one for a long time, until someone sold me a very nice gold one for 1k at Destiny's Gorge lol