What are some good online classifieds for classic bobbers or cafe bikes?
I'd try cycletrader.com, or ebay.
Or craigslist.
the problem is - the people building them are split up based on the bikes that they started on - like SOHC Hondas or Yam 650's. Then you get the triumphs and Harleys.
There are tons of sites for them, but from what I have seen, it is more for building then selling.