Strange thing.. I was just thinking about doing some "fey spells" the other night. One that grants DR/cold iron would be perfect. Let's see... Just off the top of my head, here's a quick write-up:
Fey Aura [Nod to Baxter]
Transmutation
Caster Level: Clr 3, Drd 3, Rgr 3
Components: V, S, M
Casting Time: 1 standard action
Range: Touch
Target: Living creature touched
Duration: 10 minutes/level
Saving Throw: None
Spell Resistance: Yes (Harmless)
This spell grants the target DR x/cold iron, where x is 1 point per three caster levels (maximum 5). The bonus to DR stacks with the target's existing cold iron DR.
Material Component: A handful of fairy dust.
Note that barkskin also allows stacking of natural armor bonuses, and I based this spell off that one.