I sourced the bush from one of the Aussie Mustang suppliers (couldn't remember if it was Custom Mustangs or Sydney Mustangs) and they aren't (too) hard to find.
A mistake I made was that I replaced the bush and found that the idler arm was flogged out anyway (it wasn't obvious until I re-installed it) and so if you have an old part and the bush is worn, then chances are the whole part is worn.
Brad