you can buy named varieties, but if you just want seeds then get them from the pet shop , not sure what the GM situation is with sunflower seed though ?
The striped ones are best for eating , and the black ones are best for oil . You will get oil from a striped one and you can eat the black ones , but you will get more oil from the black .
So, with only a few square yards of sunflowers you can get all your own cooking oil , all your own seed for eating and cooking , some for the birds and some for the chickens . If you do press them for oil , the waste can be fed to any of your animal stock .
You get appx 1/3 , by weight , of oil from good sunflower seeds , so if you pressed about 25lbs of seed you would get appx 8lbs of oil, about a gallon , the other 17lbs would be the waste or cake for animal feed.
cheers
Russ