Where can I get a fake marriage certificate, preferably for free?

I've looked for an answer, but mostly I've found people going on about fraud and prison. It is no worse than giving your kids fake money to play with, the key word is "fake". It is not meant to be on official paper, nor signed by a person of authority, I was going to have my sister sign it as the "judge". It is meant for fun purposes, the same way a cheap 25 cent ring as a wedding ring is. It's not like they would have an official seal or anything. So please, don't answer if it's about how I'm breaking a bazillion laws, or that I'll learn that and more in prison. It's to scare the parents because the pregnancy prank's already been done :p