I bought a soft curd draining bag from
DairyConnection.com when ordering other supplies from them a few months ago and
have used it a couple times now for making Neufchatel Cheese (seam out for easier cleaning/washing).
Dairy Connection says it is a "Re-usable muslin cloth bag. Used to drain cream cheese, quark, sour cream and to pre-drain brie, camembert and blue cheese curds. Size: 10 liter (2.5 gal)." and cost USD19 plus shipping.
The bag is very strong material, very well sewn and should be able to carry 10 litres/2.5 US gallons weight as stated, but I suspect only be able to hold slightly less considering you need to close top to be able to hang. The material has an excellent weave size to allow good whey drainage, the only negative is no drawstring at top for easier hanging from a hook. I could install a thin one in the top stitching.