All you have to know is your threading and diameter, either English 1.37"x24TPI, French/Swiss 35x1mm, or Italian 36mmx24TPI. (I have yet to figure out where they got that weird hybrid metric-English Italian BB standard!) I may even have a spare in my junk box. Otherwise, I concur with the recommendations of Harris Cyclery and Loose Screws, my two favorite on-line bike parts suppliers.
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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