Does everyone just buy extra seed potatoes at the beginning of the year for all year, or is there some sort of secret to getting seed potatoes for fall this late? I even went a few websites, and they're all sold out!

I thought about a few store bought ones, but if they're treated to not sprout I don't want to waste time try to sprout them, the lady at the garden center said just to leave them in the dark and they'll sprout on their own- but my own home grown potatoes have been in a dark spot, and none of them are sprouting!
Potato confusion
