Sigh.
Rogue Assassin:
Knife Specialization: You gain a +1 Competence bonus to Critical Damage Multiplier with daggers and kukris. Daggers also gain a +1 Competence bonus to Critical Threat Range
Requires 5 levels in rogue and 12th level.
Or if you want even earlier.
Bard Swashbuckler:
Swashbuckling: Dagger, Shortsword, Throwing Dagger: +1 Threat Range, +1 Multiplier
Requires just 3 levels in bard.
Now, this isn't any weapon, but that's only consideration with certain weapons that are already superior for crit profile. We also have to consider if the 14 levels of Paladin actually stack up against 14 levels of Bard. Are those 14 levels holding the paladin back, and Holy Sword just brings them up to parity? I'm really skeptical that KotC will be enough of a boost considering how far behind Paladins are to other melee classes.