Is it known how many of the 69 ZL-1 Camaros came from the factory with spoilers?

I think about 15.

http://www.camaros.org/9560list.shtml

Back in 68-69 spoilers were relatively new to drag racing.
Some only used the front spoiler and the rear spoiler was up for debate as to if it helped traction or added too much drag at the big end.

Bill Jenkins tells a funny story where at one big NHRA meet he put on his rear spoiler and noticed the other Camaro had grown spoilers. Then he ran the car with no rear spoiler and noticed the other Camaros would remove theirs.

The Grump said he and his crew got a laugh out of watching the other Camaro racers adding and removing their rear spoilers all weekend.