www.e9coupe.com is a good place to hang out and www.csregistry.org is another "Coupe Wanted" resource.
You should know ahead of time that a coupe is a completely different driving experience than the newer BMWs. I have an '03 530 5 speed and can attest that they are completely different machines. Many who like the feeling of the newer BMWs, which is a ride much more insulated from the world and even from the car, end up not liking the CS. The coupe is a much more driver-involved car, not nearly as comfortable and is much noisier than the modern breed. See if you can spend time in a good example first, perhaps you can hitch a ride during one of the SoCal Coupe Cruises which are discussed on the E9coupe board.