Thrift stores are the place to get the authentic look. Look for Levis, Lees, and Wranglers from the late 70's. If you're going to do the whole vintage rocker thing, you'll need a real, honest-to-goodness vintage leather jacket too. They don't make'm like they used to. While you're at it, buy a few terry-cloth polos. If you want to go fancy, older Levi's Premiums jeans will do as well. The real secrets to getting an "authentic" look are twofold: color and cut. The jeans should actually be fairly high waisted compared to the low rise of most fashionable modern jeans. The jeans should also be worn significantly tighter than American guys, and even most Europeans, have for a long while, so this look works best for the ulti-skinny (like the Kings of Leon are). And remember that people back in the 70's worked out a lot less, and the work is not going to look quite the same unless you have that lanky, no muscle tone type of body. The color (of the jeans) is also important. If you look at a lot of jeans today, there is a lot of green and black tint in the dyes used. Older jeans have a much purer blue tint, and fade to a medium blue. Check out the difference between a new pair of Levi's Premiums in say, the coveted wash, and a pair of old Orange Tabs, and you'll see the difference. Also, the material in 70's jeans was significantly coarser than a lot of the denims available today. Finally, you'll need a 70's haircut, just like those Kings of Leon guys.