Added Unbreakable Fighter 13.
Not sure if I should list this as a Stalwart ability, but
Focused Dragon Expertise grants Stalwart as an Inquisitor vs a dragon's extraordinary and supernatural abilities only, if you already have Evasion. With the
Instant Enemy spell you can make anything count as one of your types of favored enemy (you choose) "for all purposes" explicitly, so there is that for Rangers, but it still seems awfully limited and circumstantial.
There is also the Mesmerist's
Astounding Avoidance trick (works well with the
Reflexive Trick feat), but it only gives basically the exact same function as evasion - and at level 12, improved evasion - for all 3 saves. Meaning, it's only good for damage avoidance, rather than avoiding partial effects.
And lastly, I should mention the
Charger animal companion archetype, which gives your
animal companion (intended for mounts, but can be applied to any animal companion) a proper Stalwart ability, at level 15.