try the truesport link for north central area, i found things in IL:
http://www.truesport.com/Bike/2007/c...thcentral.html
as long as a race has a cat 5 category, and offers a one day license option (i think most do), then you can just show up, pay the fees, and race. no team required. lots of cat 5s race unattached.
if you want to keep racing, it's worth getting a license from USAcycling.