Can't help you specifically
Craigslist is usually the best source, because you don't have to add shipping costs- but then there's also ebay "vintage bikes and frames"
You could put a "wanted" ad on craigslist and probably have a good chance of getting a response from someone with stuff they haven't enough mind to sell but have around-
I got a Huffy cruiser frame, that matches one of my builds- last summer for $10 that I saw on craigslist.