I am pretty sure the OPs brakes are not Chorus Monoplanors (atleast the ones in the first 3 pics) since they lack the thin nut behind the cone shaped capnut. I think they are either late Athena, after Athena got the brakes from Chorus, or early Veloce.
I have some pads like this on a set of Veloce I picked up a few years ago. when it comes time to replace them I am going to use these KoolStops.
These Avids may work too. I like these two options since you can use the thick washers to mimic the thickness of the old Record style pads.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk