No, there isn't a Fullblade equivalent in pathfinder. 2d6 is the best you can do with a two handed weapon.
Is there a full blade in pathfinder? Or a weapon that a medium sized creature could use that does more then the great sword if one took exotic weapon proc.
AFAIK, a Full Blade back in 3.X dealt 2D8 points of damage and was a 2h Exotic Weapon.
The closest thing to this level of damage in Pathfinder is a Large-sized Bastard Sword. The only issue with this is that you suffer a -2 Penalty to attack rolls with using such an inappropriately sized weapon. Simultaneously, I believe there was a similar penalty that followed the use of a Full Blade, even with proficiency, so it's about the same.
Perhaps an elven curved blade. Slightly less damage (d10), but better crit range (18-20).
There was some disagreement during 3.5 as to what the fullblade was meant to represent since it was a 3e weapon that never was updated. Was it:
There are pros and cons to either approach.
As for PF, I would guess you'd have to go with the large bastard sword interpretation for official play.
thunder and fang lets you wield a large sized earth breaker as a 2 handed weapon, that 3d6 base damage.
but as far as swords go, no you cant get over 2d6 without magic.
Sure you can. Large Bastard Sword is 2D8 damage.
But Damage Dice isn't useful unless you're going the Vital Strike build, in which case it better be a Natural Weapon.
The best way to make use of oversized damage dice from weapons such as a large bastard sword, because as Jamzilla said, base damage is rarely a big deal past the first couple levels, certainly not worth a -2 penalty in and of itself, is to get stacking effects that amp up the damage dice to ever more absurd levels.
Good low level combinations are enlarge person and lead blades, which would take the weapon from 2d8 to 4d6 to 6d6. These are first level spell buffs that last a minute per level, so not a bad way to go. Given that they are such low level spells, you can easily get them via wands or scrolls, if you didn't want to pick a class combination capable of stacking them. And then if you do vital strike and devastating strike at appropriate levels, you have yourself something to be feared even when full attack actions aren't an option.
My recommendation for such a build would personally be a cleric of a god that gives you the strength domain or growth subdomain for enlarge person, or an oracle of metal for a similar lead blades effect. If you multiclass ranger/cleric you can get both spells by class without magic item dependency by 5th level, and enjoy the benefit of a high wisdom helping both classes.
I could definitely see a nature-themed divine caster with a bestial strength and a massive weapon. Either way, I would agree that a potential 1 to 6 more damage is probably not worth an exotic weapon feat and a -2 to accuracy for optimization without some extra tweaking.