Well ... firstly recheck your journal so you are sure you really have found all shards
Otherwise you should be able to do this:
enter console and type DebugMode 1
enter console and type in this command:
dm_spawnitem q6_shard
That should spawn a mirror shard at the position of the mouse cursor - unfortunally I can't make sure, because I recently just reinstalled NwN and havne't played through any of the modules myself.
enter console mode and type DebugMode 0
Should work.
Good luck.