May I ask where can I buy urethane bushings for the trailing arms, and panar rod?

Have you tried Rally Design?

Polybushing a live rear car, theres a topic thread in it own right.
- You need to make sure there is enough compliance for the axle to twist.
- I went for new rubber bonded bushes myself. Perfectly happy with it.

If the dimensions are right (suitable wide and short) anything possable but its something to be aware off.

Daniel