Make your own. Do a search on liquid urethane rubber and click on one for "casting". The ride will be firmer but not harsh. Like all urethane bushings they will push in place with finger pressure rather than pressed into place like butyl or other rubbers. Many are two part with half pushed in from each side. All the street rod suppliers offer urethane bushing as a suspension upgrade. The mold for that bushing could be made by Ray Charles in a dark room.
