Weapon Master or 2H Weapon archetypes are the obvious choices.
I suggest not throwing someone that has a 5% chance of auto-deathing a PC (x4 crit is crazy "swingy" in power) against the party, though.
If you really want to revel in the critting though, you can get Leadership at 7 and take a cohort with the Butterfly's Sting feat and a 18-20 crit range weapon. Bonus points if it's a Magus who uses his arcana to make the blade keen.