I think you are looking for something which you can add to your certificates before printing them. I used something similar years ago and although printers didn't do the gold justice in those days I'm sure they would look fine in todays printers.
I just cannot remember where I got the picture from. I had a huge IMSI collection of bitmaps etc and I perhaps got it there or from a Microsoft site.
I'm pretty sure that Microsoft still have a huge site where you can download images either free or at very little cost and I think you should look there.