Well, there's "rubber" (it's actually a synthetic petrochemical elastomer - not rubber,) polyurethane (synthetic polymer rather stiffer than "rubber,") and I've noted that some of the larger full-size trucks used bronze bushings in the leaf eyes - 1940's to early 1960's IHC LL, for instance (the bigger ones - 1-1/2 to 3 tons.) Probably rode like buckboards, but should be plenty durable.
The "greasable bolts" would have to be accompanied by "greasable bushings," which are usually poly. After all, while the elastomer used in OEM bushings is petrochemically derived, petroleum products (oil, grease, gasoline, Diesel oil) tend to be antagonistic to the polymer. "Greasable" bushings tend to be polyurethane, since petroleum products aren't anywhere near as antagonistic to polyurethane as to OEM elastomers. However, a "greasable" bolt (bored bolt with a zerk fitting) on its own won't do anything useful for you.