tourment shield

What all is reqiured to get a tourment shield at the end of nightfalls.

Armbrace of Truth

http://wiki.guildwars.com/wiki/Tormented_Shield

You can also just buy one from someone, too.

the cost to buy one is usually rounded to around 200k, 100k +23ectos or 46 ectos is the cost of a armbrace. have fun mate.

Is this someting you only have one chance to get. Or do you have the chance to farm the gemstones for the braclet.

You can farm the gems to get the armbraces. There's no limit to how many you can get.

You'll need 15 gems of each set Stygian, Margonite, Torment, Titan then give them to the Spirit of Truth, which will appear when you clear a mission area and open a gate into the next area.

You can pretty much farm any of the gemstones except maybe Titan which are found in the Foundry. And I'm only talking from a co-ordinated balanced sc team. At least that's been my experience.

its not a one time thing, your allowed to farm gems to your heats content.