Anyhow, while exploring Thousand Needles, I noticed that there were several new turtle mobs in the zone. They all seem to be around level 42-44, so I decided to go back and farm them to see if they would drop Big-Mouth Clams, the source for several types of pearls.
I focused on two types of mobs:
~ "Stranded Sparkleshells": these are regular-looking turtles that spawn on some of the few dry spots left in 1000 Needles. In particular, there are two low islands that have a nice concentration of these turtles - one is west of Freewind Post and the other is near the entrance to Mirage Flats. I rode back and forth (Water Walking FTW) between the two islands and by the time I finished one island and rode to the other, the turtles had respawned.
~ "Siltwash Terrapins": these are brand-new sea turtle-looking mobs that swim through the zone. There are less of them and they are farther apart, but worth tagging while traveling between the two islands I mentioned earlier.
BOTH of these turtles drop Big-Mouth Clams. I would estimate the drop rate at around 30-40%. During my farming run, I looted 42 clams - these gave me:
~ 1 Black Pearl
~ 1 Iridescent Pearl
~ 1 Small Lustrous Pearl
So not a terrific drop rate for the pearls, but OTOH it wasn't that great before. The bottom line is, Big-Mouth Clams CAN be easily obtained post-Shattering, and you CAN obtain Black Pearls this way. No absolute need to farm Mauradon or whatnot.
Anyway, I know this is sort of TL;DR, but hopefully this will be helpful for someone :-)
EDIT: I just farmed another 8 clams from these mobs and got 2 Black Pearls among the loot. So I'd say this is definitely a decent place to farm these suckers.