If you've gone a whole month and not seen any necropotence gear, I suspect you're not looting more than a chest every few days. The odds of not seeing a necropotence item at all in 30 days, even assuming you're only looting one chest/dolmen per day is astronomically low. More likely is that you haven't looted any "good" necropotence gear in divines or impen or maybe you haven't looted any necropotence staves or you're just exaggerating.
@redspecter23 I jump into Rivenspire every day to try to pick up some stuff. Yep, I play other areas, but Rivenspire to try to add to the Necro inventory. So, no, just bad luck.