KEH is one of my favorite resellers. But I've had good luck with all of the below. Another option to to check you local camera stores for classified. I got my RB67 Pro-S that way with 2 lenses, 1-120 back, 1-polaroid back, prism and waistlevel finders, and case for a very good price.

KEH in Atlanta
Midwest Photo
Lens and Repro