Denny, I'm not too sure about the Chicago area too much, but there is an indoor swap meet on the 22nd of October at the Indianapolis State Fairgrounds. They usually have a good turnout, with several vendors that have parts for AD trucks. I know of one vender that specializes in NOS parts that is almost always there, Paul Parlett. Harmon's is also always oresent as well.
If you do go and are not familiar with Indy, the best way I can tell you to go is to get on 38th street from I465, and go east. It'll take you right to the fairgrounds.

Bill Burmeister