Azygous has a picture of a homemade on in this article:
https://www.backyardchickens.com/articles/how-to-treat-sour-crop-and-impacted-crop-and-how-to-know-which-one-youre-dealing-with.73607/
Here are some choices for crop bras:
https://www.amazon.com/Birdy-Bra-Small-Chicken-Hook/dp/B0B664274K?th=1
https://www.etsy.com/listing/779998331/chicken-bra-crop-bra-crop-supporter-slow
https://crazy-k-farm.myshopify.com/products/birdy-bra-crop-supporter-chest-protector