Prothane bushes are the only option that I have found; I searched high and low for TRD and Cusco hyperball only to have everyone come back to say they are discontinued.
Prothane are a lot more durable and measurably harder than stock rubber. TRD were a rubber bush as well but noticeably up-spec'd.
Best place to buy Prothane bushes is Summit Racing:
http://www.summitracing.c...rothane-motion-control If you look up some of the TRD part numbers, the bushes share a lot of common part numbers with SW20's as well. Obviously the control arms themselves were different but the diameter and width for the bushing was kept common on a few spots.
You are correct also in that Toyota will not sell bushes separately.