You might check with the Mississippi Department of Prisons. They were still picking cotton by hand a few years ago. Sorry, but I don't have any contacts there anymore. All my friends there either retired or were paroled.

They were shipping at least some of the cotton to the ag museum in Jackson, as I remember, so they could have something to run through the antique gin, which was too dated to gin mechanically harvested cotton. 

There was some discussion about where to find these bags on Barry Bean's Cotton List a few years ago. Here's the link to his archive search page:

http://listserv.aol.com/cgi-bin/wa?S1=cotton-l

In the first search line, type in "pick sack". That will bring up the thread.

Owen