Lots of seed sellers have open-pollinated corn. Just google 'OP corn'.
Then watch for the initials:
OP = open pollinated
F1, F2 or Hyb = hybrid
SU = normal sugary
SE = Extra-sweet
I think OG stands for organically grown, but I'm not sure.
Most seed companies come right out and tell you which seed varieites are which, but a few don't, and I tend not to deal with them.
The most common variety of OP sweet corn is Golden Bantam, or Improved Golden Bantam.
But you've made me curious... why don't you care if it's sweet corn or field (dent) corn? If the use doesn't matter, why do you want OP seed? Usually, people want OP seed because they want to save that same kind of corn. To keep it 'pure', you have to keep it separate from other varieties of corn (by at least half a mile), as corn is wind-pollinated.
I CAN'T STAND IT... I HAVE TO KNOW!
Sue