Stencils are a great way to make single or repeat patterns with finish.
You can cut them out of any convenient material, but they always seem to want to move around while you are using them. That means the paint tends to slip underneath them and you end up with smeared edges. It is as close as the local Office Depot or Staples. Head to the section of the store that sells self-adhesive book covers. The one here in front of me is made by the Magic Cover Division of Kittrich Corp. of Los Angeles and is called Clear Cover.