Purchased TA but I can't upgrade my GalCivII Gold because of lost serial number

I bought Gal Civ II Gold Edition which came with Dark Avatar expansion.  The problem is that I never registered it (my bad!!) and I tossed the jewel case with the serial number (my bad again!!).  I figured I would be all set to play TA if a purchased it from Impulse.  However, after purchasing it and launching I get a couple of error messages about not having Dark Avatar installed and then not having Gal Civ II updated to latest version.  TA then launches ok but I am getting some random crashes and I think it might be because I don't have updated Gal Civ II Dark Avatar.  There must be a way around this...can someone please offer advice?  Thanks!