There are two ways to say this: There are no heirloom Sunflower seeds -and- All Sunflower seeds are heirlooms if that strain stays the same from year to year.
Sunflowers leap from one strain to another easily and another new strain is born and this has happened over hundreds of years. If a grower keeps that strain to itself, it makes the same strain so could be considered an “heirloom” of that strain.
Growers who are flower sellers, keep creating new strains to get different colored flowers.
Growers who are eating seeds sellers (the striped seed), grow the same strain in the same field so they get eating seeds. The strain they are growing is a developed strain for eating seeds.
Growers who are oil seed sellers (the black seed), grow the same strain in the field so they get the oil seed. The strain they are growing is a developed strain for oil.
Growers who are tuber sellers (Jerusalem Artichoke, also called Sun Choke and White Fuseau which is different but still a tuber (this one is shaped like an Idaho potato), grow these tuber ones in a separate field so they are the same every year. One buys the tubers, not seed. These are perennial so they come back year after year from the tubers and will overtake a garden.
So, Sunflowers did themselves in hundreds of years ago, because they cross strains so easily so that heirloom doesn't really exist or one could consider any strain as heirloom because the plants did it themselves. One could say they are not picky with whom they have sex. :o)
The neighbor kid that tilled my garden this year just stopped by and checked out my garden, and talked about his problems with his. Tomatoes aren't doing great this year for anybody. I'm hoping fall tomatoes produce better.
I had given the kid some of my saved cantaloupe seed and he was raving about how good they are. They really are. I saved my seed for next year from one really giant cantaloupe that I cut and ate yesterday.
It feels good having a strain that grows well in my area that I can share.
/johnny