City,
I think you are confusing all the different sweetness of corn types su, se, sh2, sy, with Bt or Roundup ready gmos. They are two different things.
Anyone can buy su, se, sh2, or sy. I think even Gurneys sell most of these to anyone. That’s the flavor/sugar you are referring to.
The insect, and/or glyphosate resistance is what is licensed. That is the infused gene which is highly guarded by Monsanto etc. Su, se, sh2, sy is not a gmo product, rather only the result of hybridized breeding.
Glyphosate resistance and Bt infused genes are the ones genetically modified. Those genes can be incorporated in any type of corn (su, se, sh2, or sy) but when that happens, the corn becomes gmo and requires a license agreement to purchase seed.
If you want to buy the Bt corn, I’m aware of two series available. One is the Performance series, the other is the Attribute series. Both require filling out the application for a license. The Performance is also Roundup Ready. The Attribute series are only Bt.
Lots of seed suppliers sell this seed, but unfortunately I don’t think any make it available in small quantities for a home gardener . I think you have to buy a minimum of an acre of seed.
That said, I don’t know how much of an advantage it is for someone planting a small garden of sweet corn to have it Roundup Ready, or Bt, which is probably why they don’t sell it in small quantities.
In other words, a small garden of sweet corn is easy to weed (Roundup Ready not as much as an advantage). Likewise it’s not as difficult to spray a small planting for earworm, so Bt isn’t as much of an advantage either, if that make any sense.
Still I can appreciate the desire for RR and Bt sweet corn. I talked with a friend a few weeks ago and he loves it. He grows just a small amount of RR and Bt sweet corn. He is able to get just a small amount for his garden w/o a license because he does a lot of business with his local co-op.
It just so happens I ordered some Performance series sweet corn the other day. Not only was the seed very expensive, but the online “paper work” for the licensing agreement was somewhat ridiculous. There were so many documents, I quit reading them. I simply want to grow some sweet corn, not have to sign documents which may involve selling my soul.