Look for Northern Indian Corn, non GMO
or
Mexican Corn, non GMO
personally that is what I am looking for as well

Check out westcoastseeds.com great place

In older days, folks used to store corn in cribs. That corn unless I'm way off was dent corn, or field corn. It's roughly the same corn that you buy in bags at the feed store (I can't say for certain if that is GMO or not).

Field corn was and is used for livestock feed. It was used for moonshine. It can be ground and used as corn meal. I'm told it is essentially hominy grits. It can be parched and eaten.
We have gotten too used to sweet corn fresh, frozen and canned.

Old style wheat can still be found. My family used to grow Thatcher (a sport of Red Fife) back when I was a kid. These days, it's pretty difficult to completely avoid cross seed. For instance, you could be growing heritage whatever on your land and the guy next to you could be growing Monsanto's latest monstrosity on his. His seed could blow over to your land, or a bunch of birds could transfer some seed to yours or whatever. Next thing you know, you have evidence of patent seed on your land and Monsanto wants their cheque.
Am I saying not to grow the heritage stuff? Hell no. I completely agree with it. I'm simply saying don't depend on it staying pure.

Well if you have a good relationship with the farmers around you, ask them for the grow dates on their gmo corn, i have it grown around me each year, somes close somes just barely visable in the distance, but as i have a good relationship, i get planting dates, pollination dates (approx) which means i can stagger plant and pick grow dates for my own corn to work around this issuse..