The company that makes the expandable bands doesn't have larger than 9mm, which is what the chickens are currently wearing.
I just ordered zip-ties from Amazon. They're cheap enough. And they have other uses, too.
https://www.amazon.com/gp/aw/d/B0BXSDV9SR/ref=ox_sc_act_image_1?smid=A3FOXFQMGBWSHB&psc=1
I use the zipties, which get changed 3-4 times as they grow.