I tried a Google Lens search but couldn't find it in the UK. Given she's a US designer, maybe it's only available over there.

Will you be reupholstering the footstool yourself? If you are then do it but if you are having it done professionally you will find it pretty pricey, in fact the same price as a brand new one. Buying a new one that fits with your decor would probably be cheaper. Next and Dunelm sell some nice ones and not too pricey as are Etsy. Footstools & more are a fab company who beautiful, sturdy footstools but are quite expensive.

Is it definitely a fabric? Looks a lot like Crucial Trading carpet.

Available on my website www.leonadrey.com