You'll have to experiment withand/or modify some modern pads. The Modolo holders I last had were ovalish where the pad meets the rim. Kool Stop makes a pad (KS-CR if I'm not mistaken) that fits Mafac holders, and many others, Campag, Weinmann, etc. A set of 4 should cost no more than $16-20. Incidentally, I think this info comes up in a serch of the archives.
Tom Martin
Oakland CA