Be sure to leave some business cards with your local realtors office. Anyone new moving to town is going to need childcare.
I would also call your local schools, the UPK, headstart, etc....maybe they keep a list of daycare providers for parents who ask.
Set up a table at ANY local craft fair, community event, block party, town wide yard sale, anything. You could hand out balloons, pencils, or cheap coloring books with your card attached.
Since you use a farm to table curriculum, I would take my veggies to a farmers market and promote your childcare there!