|11th Level Inquisitor|
Ok so easiest way is to take 3 levels of hex crafter magus and take this at your 3rd magus
Prerequisite: Magus hexcrafter archetype
Benefit: A hexcrafter magus can use mental and physical resiliency to avoid certain attacks. If she makes a Fortitude or Will saving throw against an attack that has a reduced effect on a successful save, she instead avoids the effect entirely. This ability can only be used if the hexcrafter magus is wearing light armor, medium armor, or no armor. A helpless hexcrafter magus does not gain the benefit of the stalwart ability.
hope that helps :)
Eh, just for the sake of completeness, I'll jump on the necromancy.
Ironskin Monk (Hobgoblin archetype) gets a Fortitude-only version of Stalwart (called Resilience) at 2nd level. They also get Evasion at 9th level.
This is also one of the reasons I blanket ban 3pp from my home games and only allowed closely scrutinized content.
This is the default assumption I bring to games, both that I run and I play in. Unless explicitly outlined by the GM, I don't assume anything outside of Core is available.