According to a similar question farmer Brian Scott answered, purchasing GMO seeds depends on the person who is buying them. For farmers, GM seeds are available from specific seed dealers, but unavailable for the general consumer.
“A farmer, like myself, can go to a seed dealer and buy genetically modified corn and soybeans to raise on his farm. With that purchase there will likely be a contract to sign along with information on how to properly steward the technology. For the home consumer there aren't currently any GMO options I'm aware of that one can go out and buy from, say, a home and garden center. Bt sweet corn is available, but I think you would have to contact a seed dealer who works with farmers like me or some other commercial ag entity. You can't just go to your local lawn and garden shop or big box store and get any GMO seed at this time.”
Jennifer Bearden, University of Florida IFAS Extension Agriculture Agent, explains how to choose and purchase seeds for those wanting to start their own garden. It is important to note that, as mentioned above, GM seeds are not available for purchase by the general public at nurseries or garden centers. They must be purchased from a seed dealer, and the only vegetable seeds available as GM varieties are squash and sweet corn.
However, GM food is available for purchase and consumption. Today, nine crops from GMO seeds are commercially available in the U.S. These crops are corn (field and sweet), soybeans, cotton, canola, alfalfa, sugar beets, papaya, potatoes and squash. These are the only GMO crops currently available on the market. A GMO apple is approved and coming to market. Ingredients such as vegetable oil and sugar, from GM crops are found in many foods, but the foods are not genetically modified.