I think at this point the glacial blade is likely dropped by a specific foe in a specific dungeon. Prob a dungeon that nobody farms or certain mobs are skipped due to SC.
looking at the first page you will notice that arced blade were only reported in shards of orr. So similarly glacial blade may only drop in a specific dungeon. People found arced blade because SoO is an overfarmed dungeon.
Also the mob that dropped the arced blade is a curses brigand, which can only be found in SoO.
A dungeon in norn territory that has unique mobs. I am thinking wurms in frostmaw!