Never heard of any enthusiast meets being announced on the radio. You may be talking about the Susan G Koman Drive for a cure. It's sponsored by United BMW and is on 15-Mar. I've heard they'll have an E92 M3 6MT available for test drives.
Only other large meet I've heard of is 4ngiefest 2008 (http://www.4ngiefest.com
). There'll be lots of cars (>200). They're also going to set a new Guiness record by forming the largest BMW caravan in the world. I'll be there.