I got my Leica M2 from the incomparable Leica magician Youxin Ye on ebay. Best thing I ever did. He doesn't always have bodies for sale, but when you do, you know they will be as-described and likely silky smooth.
Rollei expert Harry Fleenor occasionally sells Rolleis from his site http://www.rolleirepairs.com/rollei4sale.htm but it would probably be much more efficient to just buy one elsewhere and just have it shipped to him straight away. I picked up my 'flex for cheap off Craigslist, took it to him for his $134 shutter overhaul and still paid less than I would have from a more boutique dealer.