We have a local feed store (Olathe and Grand Junction) which has various seeds and feed. They always know if their seed or feed is organic or non gmo but conventionally grown.
http://www.westslopeag.com/ They are a local business, and probably don't routinely ship, but depending on what they have and what you want,maybe it would be worth a trip. They are very nice people. They might have organic popcorn some of the time. I think their sunflowers are not organic, but they might know a source.
I don't know how much you want to plant, but for your sunflower seeds, popcorn, wheat and barley, you could buy 25 (maybe 50) pound bags from Vitamin Cottage, though they would be very expensive. When I want to plant barley or wheat or quinoa (or
flax seed etc) I buy the one pound bags they sell for people food. I've never seen a bag of dried peas there that look like they could be used for seed.