hero4hire
Explorer
No official Bow Power Attack from WoTC sorry. 
I did find these
Power Shot [General]
By overdrawing and taking your bow to the breaking point, you can fire more powerful shots than normal from your bow.
Prerequisites: Point Blank Shot, Str 13.
Benefit: As a standard action, you may fire a single shot from your bow, subtracting a number from your ranged attack roll and adding the same number to your ranged damage roll. This number may not exceed your base attack bonus. This feat also allows you to use composite bows with a Strength bonus exceeding your own at no penalty to your attack roll.
Special: A fighter may select this feat as one of his fighter bonus feats.
Improved Power Shot [General]
You can fire an overdrawn shot with greater accuracy.
Prerequisites: Point Blank Shot, Power Shot, Str 13.
Benefit: When using Power Shot, you may fire a single shot from your bow, subtracting a number from your ranged attack roll and adding twice that number to your ranged damage roll. The penalty may not exceed your base attack bonus.
Special: A fighter may select this feat as one of his fighter bonus feats.
Rapid Power Shot [General]
You have become so adept at overdrawing your bow that you can now do so while firing multiple shots in quick succession.
Prerequisites: Point Blank Shot, Power Shot, Rapid Shot, Str 13.
Benefit: When making a full attack with a bow, you may choose to subtract a number from all ranged attack rolls and add the same number to all ranged damage rolls. This number may not exceed your base attack bonus.
Special: If you have Improved Power Shot, then the damage bonus is double the penalty to attack rolls. The penalty to attack rolls still cannot exceed your base attack bonus.
Special: A fighter may select this feat as one of his fighter bonus feats.
I did find these
Power Shot [General]
By overdrawing and taking your bow to the breaking point, you can fire more powerful shots than normal from your bow.
Prerequisites: Point Blank Shot, Str 13.
Benefit: As a standard action, you may fire a single shot from your bow, subtracting a number from your ranged attack roll and adding the same number to your ranged damage roll. This number may not exceed your base attack bonus. This feat also allows you to use composite bows with a Strength bonus exceeding your own at no penalty to your attack roll.
Special: A fighter may select this feat as one of his fighter bonus feats.
Improved Power Shot [General]
You can fire an overdrawn shot with greater accuracy.
Prerequisites: Point Blank Shot, Power Shot, Str 13.
Benefit: When using Power Shot, you may fire a single shot from your bow, subtracting a number from your ranged attack roll and adding twice that number to your ranged damage roll. The penalty may not exceed your base attack bonus.
Special: A fighter may select this feat as one of his fighter bonus feats.
Rapid Power Shot [General]
You have become so adept at overdrawing your bow that you can now do so while firing multiple shots in quick succession.
Prerequisites: Point Blank Shot, Power Shot, Rapid Shot, Str 13.
Benefit: When making a full attack with a bow, you may choose to subtract a number from all ranged attack rolls and add the same number to all ranged damage rolls. This number may not exceed your base attack bonus.
Special: If you have Improved Power Shot, then the damage bonus is double the penalty to attack rolls. The penalty to attack rolls still cannot exceed your base attack bonus.
Special: A fighter may select this feat as one of his fighter bonus feats.
