I'm 99% sure the anchors for the Mafac cantis are the same as those on Mafac Racers, which are pretty easy to come by. You can find 'em on eBay, but people seem to think they're 'rare' and ask dumb money for 'em (the anchor bit, not Racers)... If you have one of those mythical bike 'co-ops' everyone here talks about you could no doubt find one there.