Clearing The Steamvault once results in 2-6 Jaggal Pearls usually.
Obtained from Clams and Loot Bags
Much like the previously mentioned Gold and Black Pearls, these too are obtained from Clams. This time from Jaggal Clams with roughly the same, low drop rate. They are obtained from Outland creatures only, and the Bag of Fishing Treasures. They can also be fished in Isle of Quel'Danas.
Jaggal Clams are dropping from Naga and Bogstroks mostly. This means two instances are an excellent source for them: The Steamvault and Slave Pens, both in Zangarmarsh.
Jaggal Clams may also contain Shadow Pearls. These are not that valuable usually, though.
Because Jaggal Pearls are quite slow to obtain, it's possible to sell them for even 100-200g each, unless your realm is populated by bots or too many other players farming the same thing. That does not necessarily mean less profit though. For example, on my realm there was this one person selling over hundred Jaggal Pearls, for 9g ish each. I bought them all and relisted for about 80g each. Not even 12 hours went past before 10 sold. A few more popped up and they were 9g also. I bought them too. If they were 79g instead, heavy undercutting would have begun.
So competing with botters is not always a good idea, even if it means profit. Most of the time it's better to farm something else if you are expecting to be undercut.