I want to make sure I source my veggie and fruit seeds from GMO free sources. I know the following seed companies sell (to the best of their knowledge) GMO free seeds from statements either in their catalog or web site:
Baker's creek (actually does testing)
John Scheepers Kitchen Garden Seeds
Territorial Seed Company
Johnny's Select Seeds
The Cooks Garden
also confirmed the above with the source of the safe seed pledge:
If they don't specifically advertise it, I would say the odds are very good that their seeds aren't GMO-safe. It's a lot of trouble to certify that, and companies that do go through that process use it as a selling point quite openly. I would particularly think that Parks and Burpee use whatever seed stock is available; Thompson and Morgan may have a different line of seeds that they sell here vs. in Europe. This is what they say on their site
The only GMO vegetable seeds on the the market are Bt Sweet corns from Syngenta. They are not available to the general market and require a markets gardener to sign off on growing conditions. Those buying seeds in small quantities have no worries at this time. Field crops like corn, soybeans, etc are a different story.
http://www.jlhudsonseeds.net/ is committed to a philosophy that encourages saving and sharing open pollinated seeds. Besides selling seeds, J L Hudson Seeds also functions as a seed bank that anyone can participate in if they follow stated requirements. This company sponsors the Seed Germination forum on DG. Catalog entries on seeds are fascinating not only for cultural, germination and viability information, but also for the role some of the seeds have played in human and ecological history.
The problem is not buying gmo seeds so much as those containmentated by modified genes. I don't see Monsanto selling gmo plants or seeds directly to gardeners. It would be too risky since they save seed and almost impossible to check up on all backyard gardeners. However, I would be concerned that the seeds I purchase could have been cross-fertilized by a GE crop in a nearby field.