I saw a strange sword but how can i get it? Please help.

 Wile playing thou the game i came up on two carectors that had that sword. It looks like the starfang longsword and the keening blade, I saw it on one of the nights in redcliff and on the proving fighter. My qustion is this how can i get that sword because they had it in diff materials, one was steel i think and another veridium so there has to be a way to get it,right?