KTM O scale wheelsets

Got a link, or pictures? Google isn't throwing up anything for me.

Offhand & without references I'd say they probably don't fit Atlas cars, as Atlas don't model the proper bolster under the car floor, but have a deep section on the truck itself.
Atlas trucks don't fit Weaver cars, for example, as Weaver model the bolster on the frame.

KTM was a big player in early O Scale Japanese imports.  Their roller bearing trucks were nice, and the caps rotated - I think they only came in Symington style.  Your only hope is the used market - I do not see them showing up often.  They mate almost anything that an Athearn truck or All-Nation truck would mount on.