I just purchased a Harbor Breeze "Santa Ana Ceiling Fan" yesterday at Lowe's and the shoulder bolts (Preassembled to hangar bracket B identified as KK) are about 3/4 of an inch too short. The box that the fan is attached to is behind the 1/2 drywall and these bolts are way too short.
I need some about 3/4 of an inch longer.

You should be able to get longer bolts with correct diameter and thread count at any hardware store, Lowes, Home Depot, etc.