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Many cities have used bicycle parts co-ops and recycling centers like my favorite in Bellingham, WA.....

http://thehubbellingham.com/

Every time I have needed an odd bit for my Frankenbike or vintage restoration I have hit paydirt there.
Another option is hitting recycling centers, thrift stores, ect. and trying to find a similar bike from that era and type for a source of compatible parts. The only problem I have had doing this is that half the time I find a nicer frame for the project foundation in the process.
If you are willing to put some work into it you can end up with a darn fine machine for spit cheap.