thanks again.  lol the NASA analogy.
 
sorta off topic but I'd like to recommend to anyone who doesn't know about it yet:  this integration of Melodyne into X3 is stunningly cool. especially if you spring for the editor upgrade. record an audio file, say a bassline , then Without even needing to load Melodyne, drag the audio file to a MIDI track and presto audio to midi conversion!! yes the midi track might need some clean up, but how long have we been waiting for audio to midi that works this well and this simply?!
 
in fact if you take the extra time to load the audio file into melodyne before audio/midi conversion and clean up the timing and length and especially pitch correct the notes (polyphonically in Editor upgrade) you get a near perfect midi file WITH the feel that you played the original. it doesn't just convert to notes it also translates the velocity of the notes
 
so even if i play kinda bad ( which is the case when playing fast) i can get a perfectly timed audio file without time stretching artifacts etc
 
anyway...not trying to do a commercial here. just thought i would mention it in case you kind and generous NASA folks didn't know about it 

For the Steve Harris sound, the best way is a Bass Player playing strong fingerstyle on a PBass with new strings, a Trace Elliot Amp (ampeg SVT will do the trick), 4x12 cabs (a 8x10 Ampeg will also do the trick) and a dbx160 comp (that was his setting)...I agree it's one of the best rock bass sound in the world (wrathchild is just too good). Also do not forget to make it VERY loud...lol
 
I think you won't find that kind of samples since his sound is strongly related to the way he plays...He's quite a brute on his bass and most usual bass samples are typically either slaps, either soft fingerstyle , either pick play.