I made my own...
I had seen the linen lined ones, selling for large $$$ and decided that I had better places to spend my money.
If you search for bread proofing basket, you will get lots of options.
At the time, Pier1 was selling loads of baskets in sizes and shapes that I liked for proofing loaves. I lined the baskets with pieces of cotton meant for kitchen towels. I had purchased several yards of the material, cut it into lengths that would fit the baskets and hemmed the cut edges. You could also just buy untextured tea towels.
Flour the towel well, drape it into the basket, put in the shaped piece of dough then cover to rise.