Start by buying vegetable seeds, herb seeds, or edible flower seeds.

Below are some good resources for plants and seeds:

Local Garden and Plant Nurseries Directory: http://www.gardenguides.com/resources/nurseries/

Native Plant Nursery Directory: http://www.plantnative.org/national_nursery_dir_main.htm

Organic and Heirloom Seeds: http://www.greenpeople.org/seeds.htm