The traditional 110-74 BCD will accommodate an inner ring of 24T and a middle ring of 34T. I have found several chainrings on eBay over the past two years. Otherwise, you will need to buy a "microdrive" crank and to transfer your old rings onto it.
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"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