I'm rebuilding a 15-year-old rough-water floating dock held off from the
shore with 2 hinged stiff arms and cross-chains.

This time around, I'd like to avoid the corrosion and wear in steel hinges,
and I'd like to add some sort of shock absorber against the percussive
forces of waves.

Anyone know of a rubber hinge or something else that would do this job?

We're talking heavy duty here. A 7,000 lb 10x50' float, with 500 lb
6x6"x20' steel tube stiff arms, 1" diameter stainless hinge pins. Waves up
to 4', winds to 70 mph, a 15' tidal range, and 3 kt currents.