Fiat only sell the ARB as a complete assembly, i.e. Complete with clamps and new bushes.
Several companies (Powerflex and Supaflex) sell poly bushes which need a little fettling but once fitted will last the lifetime of the car. These can be fitted with the ARB in place although it is easier if the ARB is removed.
You can get rubber bushes on Ebay and a few other places which will do the job.