Just finished 3 days so far and have 3 of the items for the pants.
Jar of Ointment - cral ligi healer (Twilight Sea)
Hunted just wandering cral ligi warders in the hidden valley, and saw more named spawns after server reset (7 in 2 hours) than after servers been up long time. Aliens will leave you alone, but the rhino beetles and underbulks will attack if let them get close enough.
Mark of Meditation - cral ligi mediator (Tenebrous Mtns)
Contrary to earlier post, the mark drops off CRAL LIGI mediator, not GROL BAKU mediator. To spawn any given quest alien in Tenebrous, hunt the common "soldier" of the appropriate tribe. One of the named for that tribe will spawn after few kills, some are more common than others. Occasionally, a warlord will spawn. Killing the warlord will spawn multiple named, have not pinned down if all named spawned are same tribe as the warlord. Take a tracker with you as the aliens wander the entire zone, otherwise you will never get any Tenebrous alien piece in reasonable time. Was not KOS until after killing a LOT of aliens, otherwise bats and wolves are about the only wandering mobs that will aggro on you.
Cloud Jewel -
Got my cloud jewel off a grol baku soldier in Tenebrous Mtns. In fact it was the only quest jewel I got off any alien. I am sure other mobs drop jewels more regularly, so don't hunt the aliens specifically for them.
Ralcom's Writ - ancient sun revenant (Scarlet Desert)
Hunted all 4 sun revenant camps on the main floor of the zone. Ancient sun revenant spawned at the 2 spawn camp just to right of Twilight Sea zone, which seems to be where everyone has seen him.
Edited, Sun Jul 21 20:40:23 2002