Here are some places where you can collect information about upcoming track events:
1. The websites of the major marque clubs, such as:
BMW CCA (BMW Car Club of America)
PCA (Porsche Club of America)
FCA (Ferrari Club of America)
VCA (Viper Club of America):
MBCA (Mercedes Benz Club of America)
AROC (Alfa-Romeo Owners Club)
S2KCA (S2000 Club of America)
(You may need to navigate from their main websites to the sites for their individual chapters.)
2. The websites for the non-club organizations that hold track events, such as:
Skip Barber
Bob Bondurant
TrackTime
CGI Motorsports
Chin Motorsports
Car Guys
PDA
NCRC
Trackmasters
Panoz Racing School
3.
http://www.trackschedule.com
4. The websites for the tracks themselves (some only show spectator events, while others show all events). If you're looking for a master directory of North American tracks, with links to the track websites for many of them,
this is a good site. It's not totally complete, but it's as good a listing as I'm aware of.