On your 75+ toon with TSO, grab the void shard missions.
Find a lvl 50+, mentor them, and enter the instance (DF, Najenas, CoA etc).
Once inside, unmentor and as everything is grey, you can complete the mission and claim your shard(s) in a fraction of the time it usually takes. You can create an alt account using the recruit a friend program, which gives you TSO for free (whilst on trial) and it's easy to PL the alt to 50 (took me just over 4 hours using a SK with a Dirge alt).