Looking for "butter muslin"

I'm looking for "butter muslin", which is a very fine (90 or 100 grade) muslin cloth used for straining yogurt, cheese, nut milks, etc. It's what nut milk bags are usually made of. It's a much tighter weave than the muslin typically found at fabric stores. Butter muslin is easy to find online, but I like to buy locally when I can.

I just need it for cooking, so I can use either bulk or pre-cut sheets.

Any ideas?