The flags in the Chicago Historical Society came from the old Gunther Collection after he died. Gunther had a huge Civil War museum that he gathered items for in the later 1800s and continued adding to it until he died. CHS bought the collection in the early 20th Century. Some of it has been de-accessioned since then including flags.

I would contact their curator and see what they have for this flag including images. Their flag collection has been photographed so far as I know and they probably charge for these images.

Greg Biggs