I have had good luck on super cheap-os from China.
Order yourself at least one each of the permutations, to keep on hand. They are usually $1 or $2 delivered (how is that even possible? I know, perverse exchange rates) if you are willing to wait 2 weeks. A fraction of the Wal-Mart price, and you can get any flavor, even the obsolete ones that we collectors need.
A while back there was a thread here "Post your adapter collection" and I wanted to do it, but my multiple-dozen-item stash was scattered. Maybe I will start a new one.