I try to farm that material since 9 days, and it is a very frustrating experience.
I had farmed before more than 3000 culanda laquer and more than 2000 shimmering sand.
Those quests are ok, as you get a guaranteed drop of those mats, so it is worth the effort.
But ivory brigade clasp is so hard to get. This is even more frustrating, as the upcoming DLC will allow us to get structural furnishing plans to build small castles.
ZOS, please correct the drop rate to work like in Summerset or Northern Elsweyr as soon as possible.