www.edgeaddicts.com
Edge addicts is the official DE group for the track I believe. They do a lot of private groups, etc. They put on the Lambo bull run last weekend, and a buddy is going this weekend to COTA (though I don't know who with- maybe a private COTA seat holder event).

www.thedriversedge.net
The Drivers Edge is the biggest DE group in Texas. They do a date or two a year at COTA.

And BMWCCA does a track day every year in March at COTA. March 20-22 this year.
http://texastrifecta.com

Those are the local organizations I'm aware of. And speed hunters had that one date, which you found in the past.

Also- they are very proud of the track surface and facility. There are rumors of large bills for damages. Just FYI for those considering it.