Doom discovered a shiney today but due to it spawning a mob, he lost his chance to pick up the item, yet as a result, I mentioned a cave which contained this.... http://www.wowhead.com/item=85777/an...en-mining-pick
I'd been hunting for it a while, so we went and had a look. Doom found it. He bounced up and down on the item, yet I could not see it. He picked it up and we went on our way, however, I submitted a bug report and contacted a GM regarding the issue.
His reply, stated that these item's are classed as quest's. Once you've picked them up, you will never be able to find them again, on that character.
I highlight that for a reason, because in the course of adventuring and leveling, you may have inadvertently already picked up and sold the item.
Luckily however, the gracious GM returned the pick to me.... but I wanted to just give you folks a head's up, incase your hunting for a specific item.
I include Wowhead's current "Lost and Found" page to help you locate or even just glance at them incase you want to hunt for an alt.
Added - Riches of Pandaria achievements list - http://ptr.wowhead.com/achievement=7997
*note it's PTR currently*