Actually, the K-H brake parts have become much easier to source recently. The reason is, the calipers are shared with late 60s Mustangs.
So you can order new calipers from O'Reilly's or Rock Auto. Summit Racing sells US-made better-than-stock disks for less than stock replacements, and ceramic pads.
The used parts you will need are the spindles, the hubs, and the dust shields. There are usually some for sale in the parts forums. Any used calipers you buy are only good for cores, probably.