Got mine on Craigslist and was VERY lucky, but they are out there. As these TJ's get older there are more and more people parting them out. You could also search junkyards. I prefer them over the full doors. So light and just enough.
I almost bought a set from Craigslist this year. They were in really nice shape. They were originally silver but the owner had just the outside painted red to match his Jeep. I could see the silver around the door seals. Had they not been re-painted red they would be mine.
