G'day Aussie AB's & DL's
I have personally bought from independencesolutions and they have been very good. I buy direct from the store so can't comment on postage. They have a showroom in each state so I recommend you visit them.
The world is your oyster when it comes to plastic pants, eBay and internet stores sell everything you could ask for and unlike large packs of disposables, plastic pants are cheap to post.