You say this... but TRW manufacture the ball joints apparently, as they're on ECS tuning's website. However, there's no part numbers avaliable from there or TRW suppliers, which would include your bunnings style motor parts suppliers???
Those suppliers should have access to nearly all parts within Australia. If they can't get their hands on the parts, then all you're doing is buying from somebody else who'se imported a select few parts and is scamming the crap out of any euro car owner. Obviously it's already been decided that it's not worth stocking the parts.

As I've said; even pedders only have stock "in their warehouse" ... no branch has any in stock. If they want to sell their stock, they should supply them for a more reasonable price. How many other makes and models do you see with $110 ball joints?