Despite the photos of the prototype '67 Z/28 with a rear spoiler, it was never a '67 option.
Spoilers [front and rear] became an option [D80] during the '68 model year. There were two front designs used for '68. The early version [at least through April '68] fastened to the lower grille panel and did not use support brackets. The 2nd design was larger and used three mounting brackets.
D80 continued as an option into the '69 model year. All '69s built with D80 through early February used the narrower '68 rear spoiler. At that time some D80 cars received the wider '69 version. By March, all D80 builds used the '69 style. Early April '69, D80 was included with the Z/28 option.
There was no dealer option per se. But many Camaros had a rear spoiler added from the parts department. In production, one of the trunk lid torsion bars is stiffer to compensate for the added weight.