LMC has them but I dont know how good they are. the ynly come in a few colors but if that doesn't matter then its all good. I'm not sure if you can still get them at the dealers but if you can and thy aren't too expensive thats the way to go because it OEM so it will fit better. I know there are other places too but I forgot which ones they are but someone will probably post them.
A friend of mine just bought a set of 81-87 std door panels from our local GM dealer, around $40-$50 each. He bought the door panels, handles and armrests since his truck is a 1980 K20. I can ask him for the part numbers if you need them?