Even herbalists and miners don't go there often, and everyon else has no business to be there. Kill everything on the U-shaped ridge and then go lap back around, the naga will have respawned by then.
It's like rolling a 200-sided die every time you open a clam and hoping from one specific number. The drop rate doesn't aggregate as you open the clams. This item has a frustratingly low drop rate that will seriously test your sanity.
Comment by Vibriss DISCLAIMER: If you have the option to buy the pearls somewhere, strongly consider it before going to farm them.