audio transformer + crystal oscillator + battery = AM radio
At scitoys.com
http://scitoys.com/scitoys/scitoys/radio/am_transmitter.html
source of radio parts for this type of project:
http://www.scitoyscatalog.com/category/R.html
Radio Shack has audio transformers…
http://www.radioshack.com/product/index.jsp?productId=2103254