You gotta really hunt. I have not had luck at bike swap meets (picked up a pair of wheels and a 7sp freewheel) but never any of the good stuff. Everyone saves that for ebay so they can get premium price for it. The two local bike shops in town who DO have vintage stuff always builds them up into bikes, then sells them whole.
I can tell you though, ebay is probably going to be your best chance to find parts but be careful. Make sure the photos of the product are good, and examine them closely so you get a good idea of the condition and value of the part. Also, there is always going to be a better deal so if something pops up that you want, but is too expensive... just wait a week or two.