Can anybody suggest how I might find an inexpensive, very small road bike for a 4 ft. tall 10 year old? Something around 38 cm with 650B wheels would probably be ideal. Surely, there's some used ones out there somewhere?
Search Ebay, Craigslist, Junior cycling forums.
Search road bike listings with key words such as "youth", "junior", "kids", etc.
Or search for particular junior models such as: