Use dark leafy, edible local wild plants from an area you KNOW isn't sprayed with any chemicals or from a contaminated area. Wild crafted foods. Often older natives or botonaists that are into these priciples can get you started. This is a good skill to have under your belt anyway. There are books available too that should help you identify wild plants in your area. They will contain way more minerals than any regularily grown plants.
Organic plants are a downgrade from this but still better than regular toxic supermarket fare. Domestic organic choices would be such foods as kale and collards, juiced.