Wow! A stumper! I don't know about this 2/5 thing unless you have some real doozies... at least its tough.
There are only two "items" I know of that can only be bought, never found. The Flame Rod, and Mace. (why there aren't maces lying around everywhere, I'll never know. It looks like a common weapon to me.)
Since I don't think anything happens to Christy (who sells the mace), I'm thinking perhaps something happens to Ed Edmund who carries the Flame Rod. (He moves at least once that I know of)
Actually, I'll just go ahead and lump both those two guesses in one post.
Mace
Flame Rod