Here is my Guide to the one-off Onderon Collector Mission.
On Imperial side, you can pick up this mission in the market area of the Royal Hunting Lodge by clicking on a Datapad.
Note a couple of the items are inside tombs/crypts.
Here are some screenshots of the locations. You may have to wait for the items to respawn if they’re not there. Respawn time is likely 5-10 minutes.
Kith Kark’s Saber
King Ommin’s Exoskeleton
Queen Talia’s Necklace
Is inside a damaged tomb next to the crashed Republic ship.
Tome of Freedom Nadd
Is located inside the ancient Sith Crypt