Vigilantes gain Disable Device as a class skill.
None of the vigilante talents grant Trapfinding to allow this class to use Disable Device on magic traps.
Can a vigilante gain the Trapfinding class feature without multiclassing, campaign specific traits, or using 3rd party materials?
Not that I know of. I had asked the same question in this thread over in the rules forum and no one else mentioned a way outside those you already covered.
Variant multiclassing (from Pathfinder Unchained) gets you Trapfinding at 3rd level. It differs from standard multiclassing in that it costs you 5 feats (at 3rd, 7th, 11th, 15th, and 19th levels) but no actual class levels.
Another method is to select an archetype that grants spellcasting and uses a spell list that includes Aram Zey's Focus.
Yep, about the only other option I could find was the Signature Skill (Disable Device) feat and 10 ranks of Disable Device letting you try to disable magical traps with a -10 penalty. At that sort of penalty, it's not worth wasting a feat. Thanks for the idea though, Eltacolibre.
I find it amusing that aside from the iconic Rogue, Trapfinding or some variant thereof is available to Investigators, Alchemists, Bards, Hunters, Oracles, Rangers, Inquisitors, Slayers, Sorcerers and Druids, but not Vigilantes.
Thanks for the info about the Unchained option David. I'll look into variant multiclassing, though as it's not valid for organized play I don't think it'll fly.
Signature skill also is not legal for PFS. Only the Unchained Rogue can get skill unlocks.