If you can't find a suitable vintage frame in time for your trip, may I suggest the Nashbar touring frame and fork? I really like mine. It's aluminum, but not very harsh at all with larger volume tires. The quality is good, it handles great, and will accept any modern group without having to spread the rear stays like on a vintage bike. Oh yeah, I forgot to mention, it's a fraction of the price of the other bikes and pretty much shares the LHT geometry if I'm not mistaken. Here's a pic of mine:
