You don't say the general area of Missouri you found them but none of the Walmarts in SE Missouri even try to stock them as far as I can tell
And of course we have no Bass Pro or Cabellas or Scheels or any other big box stores who from time to time at least "try" to stock caps!
I went to a gun show in Troy mo. over the weekend. I found all kinds of #11 caps, 209 ,musket caps,as well as rifle primers .in Warrenton mo. both gun stores have cci and winchester#11 ,I haven't tried Walmart yet. Bruce