Two places to find a 1969 Camaro Z28 with a 302 engine are ClassicCars.com and AutoTraderClassics.com. You can configure your search to year, make and model and enter "302" in the keyword field.
Vintage cars can be hard to shop for, especially in a specific factory configuration. ClassicCars.com has nationwide car listings. You can search and sort the results to find many Camaros with different options.
AutoTraderClassics.com is another resource. Auto Trader is one of the first online car classifieds websites and has extensive Camaro listings. Most listing have pictures as well as descriptions. You can find cars with the in-depth information on options and overall condition.