Ah, the hunt for original rally wheels! I know it well! First look here to see what you car could have been ordered with
http://www.camaros.org/suspen.shtml#WheelsPay close attention to the Drum/Disc! The drum wheels do not have enough clearance on the inside for the disc calipers. Then figure out which months would work for the build of your car (6 months prior is the rule of thumb). Also, the different width wheels take different sized trim rings, so you will need to figure that out once you know your wheel size. Caps are normal 68/69 versions, lots of options to buy them.
Then start hitting, ebay, Craiglist, swap meets, Camaro forums, etc. Luck on the hunt!
PS, if you have aftermarket disc brakes, factory disc wheels may not fit, need to take measurements or just buy a wheel to try it.