There are many that fit the older M2 Freightliner chassis but only a few that make them to fit the S2 Freightliner. The one I have seen mentioned the most is from ExGuard.
I saw the results of a Ford 3500 with a grill guard hitting a moose cow here in Wyoming were I live. When he hit the moose, it bent the top of the grill guard back enough to act like a ramp and put that moose right up accross the hood, then the windshied, driver and passenger both injured, totaled the truck.