The reaction force is obtained as the negative derivative of the total energy (E) with respect to the reaction coordinate (several papers describe the method). You need the energy and the reaction coordinate values in the R-->TS-->P direction, which are obtained, for instance, at final of the .log file.

The gradient can be obtained from a exel work by resolving a simple equation in the form of: Reaction_force=-(E{n+1}-E{n})/(RC{n+1}-RC{n}), where E{n} is the energy in the n step, and RC{n} is the reaction coordinate at the step n. Moreover, the reaction works are obtained as the energy diference between the critical points in the reaction force profile.