I live in Georgia, USA. Our winter are mild with days below freezing. For about 10 years I had a garden full of impatiens flowers. They were so many that they even grew in concrete cracks !!!! These flowers came back years after years, perennials. Then one year they did not come back. I have been looking everywhere for seeds to replant my perennial impatiens. Please, help. Thanks

Those were self-sowing annuals...
In Georgia, impatiens are positively weedy in an irrigated garden.

They spit ripe seeds out everywhere.

I suggest patience, Im not seeing them yet either, but they always come back, no matter how many wheelbarrows full of them I pull.

If its been a number of years without them.... Just get ordinary seed... Or pick up a six-pack at the nursery.

My guess is downy mildew. It's going around these days. It's been hitting mine every other year. which means that impatiens seeds in the ground stay viable for two years. Last year was a great year for impatiens here. The year before I had none. So far this year is looking good. Fingers crossed.
Are yours perennial in that the plants survive your winter or do they reseed like mine?

What kind of Impatiens? There are various species. The most common ones I've seen discussed:
Busy Lizzy (Impatiens walleriana)
New Guinea Impatiens (Impatiens hawkeri)
Balsam (Impatiens balsamina)
Himalayan Balsam (Impatiens glandulifera)
Orange Jewelweed (Impatiens capensis)