Antique radio dealers. If radios are their sole business, however, they should be more willing to take returns if you're not satisfied, and they may offer guarantees on sets they have restored. They should offer a good selection, of course, and they may even help locate a particular set for you. I visited an antique radio store during my 1997 summer vacation . A great place to shop, if you enjoy buying radios at highly inflated prices.
Online auctions tend to be extremely expensive, however.
If you compare Internet auction prices to prices in other venues, you will routinely see people spending much more for common radios than they would spend for the same item at a swap meet or the typical ARC classified ad. I don't have anything against auction websites. If you live in a desolate part of the world, they may be one of your few choices. And Web auctions occasionally feature truly rare items that you might not find in months or years of searching. For the most part, however, you can find the same radios at much lower prices in the sources listed above.