If I remember correctly spoilers started towards the last half of the 68 year.
"The spoiler option was not available in 1967 on any Camaro. It became available as an option on all cars (except those with a rear antenna) in 68-69. It was not mandatory on any car, except for the 69 pace car replicas and later 69 Z's. The narrower 68 spoiler was used on the 69 Camaro up to January - March of 69, when the wider 69 spoiler was phased in." The previous in quotes is taken from Camaro Research Group.