Allen Galutira
agalutira@lvcm.com
Grand Touring races have different subgroups. To race a car in one of these groups, the car has to be mass produced to a minimum number of units by the manufacturer. This keeps tuner cars and factory purpose-built one-off cars from racing. What Pontiac did was produce the GTO in the bare minimum number required so they could participate in GT races. That's why they're so hard to find.
The Camaro Z28 was also born from homologation rules, though forget what kind of race they built it for. Sales and demand were so strong in the first 2 years that GM decided to make the Z28 a full production trim level instead of keeping it a homologated limited production one.