Lost product key for FSX Acceleration Expnsion pack

Can anyone help me? I've reinstalled FSX on my laptop and wish to load the acceleration pack, but the problem is I have lost the card containing the product key for the acceleration pack. Is there anyway of geting around this, or do I have to forego the pleasure of the expansion pack. The other problem is I have many free downloads from this site, but many don't load correctly without the expansion pack.