The only weapon I know of that uses the character's unarmed damage instead of the base weapon damage is the Scorpion Kama in the MiC page 201.
Pole Fighter is the feat Waazraath mentioned.
If weapon size rules can be worked with then a medium creature with a large kama treats it as a 1-handed weapon and can thus use it two-handed for 1.5x str to damage. It's a -2 to attack though due to the improperly-sized weapon.
The Exotic Weapon Master's Uncanny Blow trick might also work in that case to grant 2x str to damage, but a DM can say that since a properly-sized kama is always a light weapon then it won't work that way. If you want the kama to work then simply add the Sizing enhancement to it.
