Another option to 3d printing (I wonder how well this works for gears on consumer-level printers?), is to print out the gear pattern on label paper, and stick that onto a piece of plexi glass. Then cut out the circular shape, and finally use a triangle file (along with a vice) to cut the gear notches, using the printed label as a guide. I did this once for a gear for an older Okidata dot-matrix printer used for multi-part forms.