If in Bayside Melbourne, then head down to Laundry Box Organic Dry Cleaners at 319 Bay St, Port Melbourne, they make sew them on premises with fab fabrics available :)
There are tons on eBay!
There’s a few businesses, not for profits and social enterprises listed here that help charities and communities in need :)
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Evie & Archie are one of the few places who seem to have a lot of stock available:
Billy & Co on Etsy have pretty masks and are updating their page daily: https://www.etsy.com/au/shop/billyandcoau
Mad Maddy Masks are on back order but are donating their profits to a kindergarten in Seaford: https://www.facebook.com/madmaddymasks
Melboune based fashion designer eatmedo are making pretty reversible masks for $30 each https://www.eatmedo.com/collections/new/products/reversible-face-masks?variant=31932780380278
Flashfomo have a lot of cool designs in stock starting at about $16, and if you buy 2 you get the 3rd free! https://www.flashfomo.com/collections/face-masks
Hew clothing also have a few nice printed ones in stock currently https://hewclothing.com/collections/face-masks
Hope that helps you out!