You can get clear (or grid ruled) thin plastic sheets for cutting out templates at JoAnn Fabrics. I got one for 99 cents or $1.99. it's 12" x 18", so you have room to cut more than one or to re-cut if you make a mistake.
Find a template online, resize it in Windows Paint (using the Image menu, either the Stretch/Skew or the Attributes option) and print it out. Tape it to the plastic and cut.