The WTB approach can't hurt, but in addition to asking to buy, add that you'd love any hot tips if someone sees something. You'd be surprised how some people will try and help out. Oh, and might not mention you're looking so you can do a fixie conversion--just say you want something from the 70s/80s in your size. Saying "fixie conversion" in a bike town like Portland will automatically add 20 bucks onto the price .