Trader Joe’s sells organic zucchini (also known as summer squash) on a consistent basis, and I find it tends to be less expensive than at the supermarket/grocery store. Some of the zucchini (as well as some sweet corn and papaya*) grown in the US is from genetically engineered (GE) seeds. If you want to avoid this, buy organic.

*All commercial production of GE papayas is in Hawaii. However, most of the papayas sold in the continental United States are imported from Brazil, Mexico, and the Caribbean (and not genetically engineered).