A guy with a suburban shows up at all the chicago region scca events and sells them. PM Magnetics (or P&M, cant remember for sure) if you want to see him in person, he'll most likely be at the chicago region autocross in joliet on sunday, at Rt. 66 dragway. I wont be there, event is full already!
edit: sorry, i dont have a url or # for the guy
edit again: I actually made my own, i bought paintable magnetic sheet from a Michael's arts and craft store, made the numbers on the compter, printed them out, taped them to the magnetic sheet, cut them out with an exacto, removed the paper, and painted.
heres a pic from an ice race in january:
mark