Hi, and welcome to the site. Eloc431962 is right, 73 and 74 interchange. Try the National Nostalgic Nova website: CLICK HERE
When in doubt, Google "vintage Nova parts". These door panels only come in black, but you can make them any color you want with SEM products.
Also, please don't start a thread with the words "help" or "need help". All the mods have been asked to tell everyone not to start a thread that way because if you learn something that is useful to others, the search function won't pick it up. I'm going to change your title to "'74 Nova Door Panels".