Heavier springs for sport resi shocks

I'm looking into new shocks for the rear of my rhino. It's sagging due to weight of 4 person cage and all of the shit I pile in the back while riding. Before I buy new shocks I was wondering if they make a heavier spring to replace the stock spring. My shocks are the sport resi shocks on a 09 sport rhino.
Thanks for the info. Mike