University of Utah - Go Utes!
I second contacting AEG. Regardless why the cube disappeared they may send one in the name of good customer service.
Agreed. Not long ago I lost a piece to Bottom of the 9th. I contacted Dice Hate Me Games, told them I lost the piece, and asked if I could buy a new one. Within a few days I had a replacement piece mailed to me free of charge. Wow! Sure made me a bigger fan of the company. I would have been a fan even had they charged me. Regardless, even if the lost piece is your fault (like mine was), it is worth reaching out to the company.
That said, the cubes in Istanbul are of course very generic and likely easy to replace on your own. If I'm not mistaken, the cubes for the post office are not even painted.