When its time to stockpile seeds for my survivalist garden, I usually get my heirloom seeds locally. There are 2 feed and fertilizer stores here in town that sell seeds – all kinds of seeds. Instead of getting seeds in packets, the stores get their seeds in burlap bags, and then sell the seed by the ounce. I like to go to the stores, talk to the people there, see find out what are the best types of plants to grow in my area, and go from there.
The local stores usually know what will be in short supply before spring gets here. They will put their orders in several months ahead of time, and the distributor will tell them what may not be in stock. This information is then distributed to the local gardener faster then you can get it through the nation news.
Most of the time, the people working in the feed store are pretty knowledgeable about the different types of seeds they have in stock, whats heirloom / open pollinated and whats hybrid. All you have to do is ask. One of the local stores usually has 5 or 6 types of corn in stock – field corn, sweet corn, G90,,,,,. So might pick up 1/4 – 1/2 pound of corn one year, then the next year pick up a different type of corn.
Also, while your at the store, be sure to ask about the local pest, and what people do about them.