I've got a 1985 Trek 520 that I'm rehabbing to sell, but it's 19" c-t (a pinch over 48cm).

If you're handy with the mechanicals, you could always find a couple bikes, fix them up, sell them, and use the proceeds to get a decent bike for yourself. All I can say is, keep checking yard sales and Craigslist. Eventually you'll find something that suits you.