There are reproductions of the old feed sack materials available now on the market. But it is quite possible these are from the sacks of long ago given the age of the blocks.
Elenore burns has a book out called egg money quits that might have some of the information about them in there. My aunt told me about them long ago. She had a long low building out back and I asked her what it was. A chicken coop. The government actually subsidized these home businesses during the hard times of the depression, or right after it. My memory of that conversation so many years ago is a little fuzzy. But, I remember how she had said many girls would not have had a new dress for school if it had not been for those feed sacks.