The University of Missouri and University of Illinois jointly published a 2010 guide to local St. Louis Area Farms that is available online: http://extension.missouri.edu/ecregion/market/MarkettoMarket2010.pdf.
If you are a resident of Illinois there is an excellent PYO/Farm Market site with powerful search capability at http://www.illinoisfarmdirect.org/index.html
Or consider the Illinois Market Maker directory http://www.marketmaker.uiuc.edu/