Cut them from extruded foam, can easily round the corners as needed.
Good luck,
Richard
A quick searched yielded this:
The cotton was wrapped in jute (a heavy burlap fabric) and bound with 6 heavy metal strips. The size of the 500 pound cotton bale was regulated by the US government to be a standard size; 56 inches long, 48 inches tall and 30 inches wide.
There's some images HERE
Wayne
I've tried several times to get a good HO measure for the size of old burlap covered cotton Bales. I'm not satisfied with what I've been able to find. Anyone have a size you've used?