Michael,
I understand that the Library of Congrees has the Post records for the GAR. So if you have the post number, you might contact them. You might also try contacting the Illinois State Archives in Springfield to see if perhaps they have copies of the Illinois records. One other thing would be to write Jackie Wright at the GAR museum in Springfield and she if she can help you. I would love to have a copy of the Post 30 records, that was the post Grandpa ALex belonged to.
Frank