Velo Orange sells some nice levers with stainless steel clamps that don't look like they belong on a mountain bike.
I had these cheap Shimanos on my 1971 Gitane Tour de France and they functioned perfectly with the Mafac calipers, but they were just too modern and mountain bikey looking for the bike and I replaced them with Mafacs. You can't buy them with the silver adjusters. Those are from Problem Solvers.
Old Weinmann levers work well, too.
