From CRG:
Two vendors are making the correct truck spatter paint for first gen Camaros. Larry Christensen at Camaros Plus (303-278-8536) in Arvada, CO and Brian Henderson at Supercar Workshop in LaTrobe, PA. Both are the accepted standard in concours judging and pretty damn close to the original. A professional pressure gun is needed to apply this paint. If you are hoping to find the right stuff in a rattle can, forget it.
Camaro High Performance also has it.
This post is from '07 and I'm pretty certain any other rattle can today is not correct. It's just spatter paint. If there are any updates or other vendors selling correct spatter I'd like to know.