Pretex wasn't available in Australia either, but an enterprising APer
found a supplier in Europe and imports it. You could probably do the same, trade wars notwithstanding.
djm there's concern from some quarters that waterproof paper is 'too yellow', and some organisers are going back to the dark ages as a result. As far as I'm concerned, better yellow* than reflection off a shiny plastic bag.
*Pretex is actually off-white, not a hint of yellow.