To me, there's two kinds of gun buying. 1) There's a gun for sale, a regular cataloged gun, and I think it's something I want, so I buy it. 2) I'm hunting for something unusual and different on the used market, and when I come across it for the right price I'm going to buy it. 2a) Go on Gunbroker and pay high retail (or more) for an unusual gun.

In the #1 category all I can really think of is a 617.

#2 category is the aforementioned K22/17. I happen to have a K22 I hunted for. If you're looking for something really different, find a .44 Special like a Lew Horton 24/624, a 696, or 296Ti. Or a snub 657 (.41 Magnum) maybe. Neither will be cheap to shoot. In that arena, maybe a K38/Model 14 even though you already have a .38. Much more enjoyable to shoot than a Model 60.