Found a company in Australia that does the LS400 bushes in Polyurathane, don't know prices but they can be found here

http://www.fulcrumsuspensions.com.au/

I have extracted the part numbers from the downloadable catalogue (22MB) so you don't have too!

Lexus LS400 Sedan
12/1989 - 10/1994
Front Control Arm Upper - Inner Bushing SPF1352K, kit contains 4Bushes&4Tubes
Rear Trailing Arm - Rear Bushing SPF2249K, kit contains 4Bushes&2Tubes

Sorry later model people, you were not listed, but might be worth asking anyway.

Happy driving,
Leadfoot

Good helpful info....will keep and hope I never need it!!