Complete Warrior feat: Power Critical
Requires: Weapon Focus with relevant weapon, BAB +4

When using the weapon selected, you gain a +4 bonus on rolls to confirm critical with that weapon. You may take this feat multiple times, and may select the same weapon or a different one. If you take it with the same weapon, the effects stack.

That's the only thing I know of. That said, I don't have any homebrew sources.