As to the mill - I think it is in Humboldt, NE. I live less than 60 miles from there. If I watch, I can usually find flour in fabric sacks at the local grocery.
For information on feedsacks, there is this:
http://www.youtube.com/watch?v=bvOM2Q7G2DQ
and this:
http://www.youtube.com/watch?v=1iEoF...eature=related
Videos of Gloria Hall presenting a talk for Andover Schoolhouse. (I think that is a presentation for merchants who sell Andover fabric lines.) She gives a good explanation of the history of feed sacks and the development of fabric for the sacks. (They had to come up with good quality fabric to hold the products in the sacks. So, while the print may have been found only in the feed sack lines, the fabric was not as inferior as some may believe. It is not, however, like the quilting fabric we buy today. I think fabric quality continues to improve all the time.)