hhere's my response to your question:
Hey Lxxxxxt,
Seeing all the funky old bikes around town, there has to be a source. City Bikes on E. Burnside at 8th or so is a used bicycle co-op. You can find bikes there, or if you need cheap or obsucre parts to fix up something found elsewhere, they are the source. A little nicer is Sellwood Cycles, they sell bikes on consignment and will generally have nicer stuff than City Bikes, but not necessarily fancy. There is also North Portland Bike Works on Mississippi or the Community Cycling Center on Alberta. Both good sources.
You might also check portland.craigslist.org they have a used bikes section that is sometimes good.
My bro has a couple bikes for sale, but they wouldn't fit you.
I hope this helps.
- Pete