I keep 1000 in my drawer my loading room of course dry temperature controlled etc. any I plan on storing for extended periods get vacuum sealedAs @wv270wsw mentioned they don't last when they become available anywhere just like the newer powders. You just have to keep looking and hoard up when you find them.
Last time I saw some I bought 5000 of them between Federal GM210M, GM215M, GM205M, WLR and CCI. I recommend you do the same. I still have primera that are 9 years old and work perfectly, I store them in a cool dry place with silica packs.