1995 Ford F53 Thor Class A leaf spring question

Hi there, regarding 1995 leaf springs bushings on the Ford F-53 chassis. I have gone with polyurethane ones for all my sway bars, however can't seem to find anyone that makes polyurethane leaf spring bushings. It already rides like a delivery truck so comfort isn't that important, I want the suspension to last a long time.

Anybody have any ideas of where to source instead of using the OEM rubber ones? I've searched the web to no avail....