Found my loupe:
Amazon.com : Kamerar MagView 16:9 16/9 3.2" LCD Screen Viewfinder View Finder LCDVF For Canon 5D MarkIII Canon 1DX : Camera & Photo
Kamerar Brand. <$50US.
Fits the K3. It is made to fit a 3:2 aspect ratio. Two sturdy metal frames to attach to K3 body ...nice to have a back-up. The adhesive strip is not strong enough. No surprise. I carefully placed a bead of black silicone sealer around the perimeter of the attachment frame and let it set over night. A nearly permanent attachment, which can be removed (with some elbow grease) to return my camera to original condition. The loupe attaches magnetically. Really convenient. However, the metal strips built into the loupe body may not have been glued in place properly. One metal strip fell out on mine. I glued it back with some contact cement. All OK ... for now.
Next, diopter adjustment. If you don't attach the camera to a solid tripod diopter adjustment is a three-handed affair because the adjustment ring is very hard to move. Good in the sense that the adjustment will not shift over time. Bad in the sense that, if you don't have three hands, getting the adjustment right-on is next to impossible.
End result, very good. I am very pleased with this loupe. The price is attractive, The optics are good, and it is really easy to use.
Hopt this "review" will be of use.