Did you look on Etsy ?
https://www.etsy.com/au/market/adult_headbands

Try stores such Myer, Sportsgirl.Portsman where they sell women clothing as well as accessories. They are everywhere , and you need to search to find your own taste.

try a hairdresser. some stock things like this still. why not do what i do and use a bandana. wide range of styles and colours plus you can wear the bandana in a few different ways.

Another great place to look would be craft markets.

We buy a lot of our headbands and head wraps from a shop called top knot girl. Her stuff is hand made and fits newborn to adult. http://www.topknotgirl.bigcartel.com

The chemist warehouse has some nice ones, heaps on eBay too. Some markets have them

Apart from the chemist, where they are quite cheap, try local arts and craft markets. Someone will make and sell them. They will make you ones to suit your specifications if you ask them? The bonus of being local is you can try before you buy. I often get people to make things for me!

try ebay, i usually can find everything i need when i can not find it anywhere else. But pay close attention to the measurements if buying from overseas and allow a few weeks for postage. Its also a lot cheaper than buying them from a shop.

Maybe google and have a look online to find some styles. Also, I have found some stylish ones at my local chemist. They seem to have a range for all ages and all styles too. Might be worth taking a look. The price is reasonable too.

Try Priceline pharmacy or similar – they have a good range.