If the idea of buying used harmonicas doesn't turn you off, check Craigslist and eBay. I've been frequenting our local Craigslist looking for some cheap percussion stuff to put together a one-man-band rig, and someone had a collection of around twenty older harmonicas for sale not too long ago at a very fair price. Finding anything would be a hit-or-miss (mostly miss) proposition, but it still might be worth a look.