Schwinn Sprint = Huret. Any front derailleur designed for a Varsinental or similar electroforged or welded small-diameter gaspipe frame should work fine; the big incompatibility with the rest of the world is the unusually small required clamp diameter. You can also get creative and adapt standard derailleurs with shims, as I did with SunTour downtube shifters when I had a Varsity.
__________________
"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069