SAA Mom,
For children and adolescents you can't do better than
Dr. David A. Margolis at the Children's Hospital of Wisconsin.
For adult practitioners, there are quite a few midwest centers with SAA expertise. The Marrowforums
Treatment Center Map lists many well-known and respected centers that have bone marrow failure experts, many in the Chicago area and others in neighboring states. Click "Illinois" to zoom in on your area.