Did a search, and I have to agree with Nerull. Adamantine (which is the proper spelling BTW) is not random treasure at all (not in the treasure scripts), and in Logar's case it's in his inventory all the time. Haven't located all the stuff yet, as the search function in the toolset can only search one area at a time
It could be that there is a line in one of Logar's scripts which causes the adamantine to disappear from his inventory under certain circumstances, or at random, haven't searched those yet either.