I have some NOS red 42mm 4-bump weinmann pads that I was saving for a restoration, but I'm not sure there is any such thing as "soft, supple, fresh" pads from the 1970's, no matter what anybody says. Rubber products leach oils and change composition over time and get hard/brittle, even when stored in the best possible way. Just look at "new" tires on any 1900 bike in any museum ...
If you were looking for a replacement pad, you might want to look first for red 42mm 4-bump weinmann pads, then black 42mm 4-bump dia compe pads, then some other variant of weinmann pads.
Luckily, there is a modern product that is the ancestral descendent of a weinmann 36mm brake pads. Jagwire is making black "X-pads" which are 40mm (vs. 36mm) weinmann-pattern pads. Your original 4-bump pads are 42mm. So these new X-pads are 2/3 between original weinmann X-pads (36mm) and weinmann 4-bump / 7-bump centerpull pads (40mm).
Best of all, they are available everywhere at low prices and they work great. You might want to pick up a set of 4 (should be $4-$8 at LBS) to use until you find the perfect period-correct pieces for your weinmann brakes.
http://bicyclewarehouse.com/
I looked for a long time and never found a decent red clone pad/holder for weinmann brakes.
Weinmann brake-pad holders are very difficult to find. I'd pay $2/ea if someone had a stash of them ...
- Don Gillies
San Diego, CA, USA