This instructable shows you how to make your own with just a computer, printer, paper and transparencies.
I'm assuming that you have the Gimp image editor installed. Hopefully you can translate this as needed for other programs.
Step 1: Create the base image and gridlines
Create a new layer called 'Grid 1'
Select that layer from the layer dialog
Create the grid by selecting the 'Filter' menu then 'Render' -> 'Pattern' -> 'Grid'
unlock the horizontal and vertical settings for width, spacing and offsets.
- Width 0,18,0
repeat for layers 'Grid 2' to 'Grid 7' using horizontal offsets of 3,6,9,12,15 and18 respectively.
Step 2: Add animation frames
(there is a discussion at the end on picking existing animations)
If you don't have an animation, create seven empty layers.
Call each layer of the animation as 'Image 1' - 'Image 7'
Put each image layer below a grid layer. (i.e. 'Image 1' goes below 'Grid 1', 'Image 2' goes below 'Grid 2', etc.)