Return of Reckoning

Hello Everyone.
Ive completed my influence rewards for C&T for awhile now. But ofcourse their are some of the weapon rewards i didnt choose that i would like to try.
I seen this vendor in the back in war quarters who has all the influence rewards from C&T and requires a Sentinel Shard in order to purchase them.

How do i get these Sentinel Shards or is this vendor not operational bc i have never seen these shards before.

Thank you to anyone who explains this for me.

there is another vendor next to him that you can buy a shard by trading in your weapon + 40 g

i think