how do I add a COM port to a windows 7 computer tower, trying to hook up a commercial weight scale and no port

The quickest way would be to run a search in your local e-Bay site for "COM Port PCI" and see what shows up. Do you know what connection the scale has?

Do you have a spare PCI or PCIe slot in the box?
 
Thanks, for the help, I do have a port that is installed, for what I do not know, but I think I can replace it with the 5 over 4 configuration I need for the scale access site.