The Early Television Foundation website has a Classified page, which includes a "TV sets wanted" section:
http://www.earlytelevision.org/classified_page.html
You could also place a WTB ("want to buy") ad in the VideoKarma Classified section.
Harry Poster is another possibility:
http://www.harryposter.com/vintagetelevision.htm
Here are two eBay categories where old TVs show up:
http://www.ebay.com/sch/Television-Sets-/3638/i.html
http://www.ebay.com/sch/Televisions-/73374/i.html
Most of the TVs you'll find are unrestored (not working). TV restoration is not something the average Joe can learn overnight. If you don't find one that's already fully restored, you could buy an unrestored one and then pay someone to restore the electronics. This article has some advice about finding repairmen:
http://antiqueradio.org/howfix.htm
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
P.S. The name is spelled Capehart, without the extra "e."