I have seen templates for doing One Sheet Wonder card collections using an 8.5x11 but not for 12x12.
The concept behind One Sheet Wonder (OSW) is to stamp an image randomly all over a sheet of cardstock. Then cut it apart in various configurations giving you mats for 12-15 cards. I wanted to do 12x12 and instead of stamping CS, I am planning to use printed paper and then cutting CS mats to coordinate. (Yeah, I've been known to reinvent the wheel and do things backwards hehe)
So here's the pattern I came up with. Feel free to modify or post a link to your favorite version and the cards you make.