What about the Lower Mississippi Collection at the University of Louisiana in Baton Rouge? Have you looked at their website yet?

I was able to find a carte-de-vista photograph (through one of the viewers on this message board) of my gg-grandfather that was paroled before he went to Johnson's Island and served his time there.

UoL has a lot of items scanned on their website about Port Hudson; maybe there is something there about parolees.