It's weird, on some playthroughs of the game I'll get some quests that I didn't get the last time I played, yet the next time I play through the game I won't be able to get that same quest again, doesn't matter if I'm LS/DS or Male/Female it's just some quests don't activate and I don't know if they are from in game glitches or what.
My advice would be to do what the above player said and try to get Samham to give you a list of all the items he needs, 3 in total with the first one being from a plant in the Ithorian compound. Once he tells you what you need don't go get the stuff yourself, instead go to Lt. Grenn and he'll get you everything you need. From there just do it as it says and you should be in good hands.