I can't be sure what you are calling a bushing but the only thing that is on top of the spring is a plate that the u-bolts are clamped to. Over that and attached to the frame above the center of the sping is a rubber stop block. The spring itself sits on a pad that is welded to the axle housing.
The only "bushings" used are on the pins at the spring ends where they attach to the spring hangers. I hope I have descibed this well enough to clear it up.
You can get all of it at
www.lmctruck.com and several others like Brothers, ChevyDuty, etc.
