Field corn varieties
Here are some blog posts on open-pollinated corn varieties that were written about in our blog:
One of our Master Gardeners had good luck growing Floriana Red Flint Corn for making polenta (from Southern Exposure seed Exchange). We don't know of any companies in MD selling open-pollinated corn varieties.
You may want to also check out the Seed Savers Exchange: https://www.seedsavers.org/