Rubber bushes for M12 3R

[D15]

I need to replace a worn rubber bush for a rear shock absorber before this M12's next MOT. Does Noble themselves still provide parts like these? Or would I be best off asking a dealer (geographical location not important)? Would it make sense to replace both sides at the same time? And has anyone tried an alternative to the standard item, since a different material, e.g. denser, might make a difference to the feel? Finally, for a not particularly mechanical dude, are they straightforward to replace? Thanks for any answers.