These boards really need a search engine!!!!
Anyways its been posted before (its not your fault, see above).
But the drop rate is either bugged at times or its very rare. In my 20+ runs now ( I stopped counting) I have seen it (juggernaut chest) only once. And marauder twice. No pants or helmets.
Advice: if you want the juggernaut items to drop, try being the juggernaut profession story mode. I.E. If your in a group of hey yous/LFG random teams; be the first one to run into the story LOL. Then its yours. I heard that sometimes works.
The one time I saw it (4th run), it was my story and another juggernaut player looted it. So I wasnt too mad about it.