That's a new one on me. I wonder that the last owner was cleaning it with to degrade the rubber? I've seen boats from '95 and the handles are fine.
Anyway... unfortunately... no... They don't have replacement rubber. But one thing that comes to mind is... clean the old rubber away, and get some tool dip, or even that fex seal dip. (seems to be very thick) Then... just recoat it.