Hey Rob.. If I had to take a guess, Id say that Gabe modeled this for his own personal use.  I could have sworn I remember seeing this set in the store.. but it was so very long ago.  A couple other artists come to mind when I look at this, Mec, Val3dart ( though their name was different back then) Xurge - all made similar items, just not the exact replica.

http://blackhearted.deviantart.com/art/Not-Quite-Fully-Armored-117276882

This is what leads me to believe it was not "packaged content.  Pity cause that helmet is awesome.

Im guessing you are looking for older figures.. and if so, there is a nice hoplite pack at daz for the old m3.. and it has potential with proper texture maps.