Search for clues as to the current disposition of Talvash's necklace within Uldaman. The slain paladin he mentioned was the person who had it last.
A competitor of mine started a rumor that my necklace cursed the paladin. Needless to say, no one wants to buy cursed items from a jeweler.
<name>, I'll make you a deal - find the gems and I'll reassemble the necklace, so long as you'll advertise that I do NOT make cursed items!
Try looking for clues in Uldaman; maybe see if the paladin's body is down there, since he's the one who we know had it last! When you find the gems you should use this; it'll allow you to contact me here in Ironforge.
Remains of a paladin: Reading the journal reveals that after much effort, the paladin had identified the location of all three missing gems:
The Shadowforge dwarves hid the ruby in their barricaded area as they battled the Troggs for control of Uldaman.
The troggs stashed the topaz in an urn located near some unusual inhabitants of Uldaman - Alliance dwarves!
Finally, the trogg elder himself took the sapphire as his own.