If you're an OEM System Builder, you can request a replacement media. They'll need the COA, which can be found on the label printed on your computer. It's under where it says product key. That way you'll have your CD to whom you're selling it to. Though, I do believe it's OK to sell without the media.
You can go here to fill out the form:
http://oem.microsoft.com/script/contentpage.aspx?pageid=555744
Hope this is somewhat relevant
//edit//
Note to self: Read entire thread; just saw you don't have the COA, D'oh!
