Heritge seeds can be purchased in most countries. Also, go to villages in your country and you'll find people growing their own food. Ask to buy from them some seeds. Swop excess seeds with friends and neighbours. Again, it is a matter of how much keeping your family healthy means to you.
Maybe, how much it matters is not the key factor with most people, ignorance is.
On a piece of land, about the size of a bed, I grow tomatoes, onions, okra, carrots, cauliflower - and in a couple of pots I grow sweet potatoes (healthier than potatoes and the leaves can also be eaten.
Do you know how easy it is to grow granadillas? They are extremely healthy to eat.
Stop and think and you'll find your own ways of solving the problem.
I know that. I'm farmer my self and do a lot of things with my land. It is getting harder and harder to find heritage seeds (I have my own stock and replenish it every year). And protecting your crops almost impossible without chemicals (I grow Nettle and use its fermented state to repel bugs natural way)