Have you had a look at the Cancer Council Shops?
Their stuff is always reasonably-priced, certified SPF, and their website lists hat sizes up to 63cm: https://www.cancercouncilshop.org.au/collections/hats?filter.p.m.custom.hat_sizes=63cm&filter.p.m.custom.hat_sizes=61cm&filter.p.m.custom.hat_sizes=60cm&filter.p.m.custom.hat_sizes=59cm
Their website lists a 'Kiosk' in Penrith, but I'm guessing that might have a limited selection, in which case the nearest 'Store' is in Hornsby: https://www.cancercouncilshop.org.au/pages/store-finder