harven's extended stats does, in fact, give that information. I know, because that's what I use.
I found one that may do what you ask: MitigationPercent (with working penetration stat) ( https://www.esoui.com/downloads/info984-MitigationPercentwithworkingpenetrationstat.html ).
It has not been updated since 03/29/2017. So it may not work.
My version of harven's extended stats actually has percentages, so perhaps you have an older version? I very much saw percentages on anything of mine that had percentages. I doin't have a screen shot at the moment (and won't go in game until I wake up tonight), but I know I saw percentages on mine when I looked at it yesterday.