Just about any invitation card design from the website can be converted into a magnetic design instead, and of course, custom designs are available.
4x8 inches is also another magnet size that isn't actually priced out on the website; Projects that require custom/random magnet sizes are becoming more common. One of the advantages of Save the Date Originals is exactly the fact that custom sizes are available. Any rectangular size up to 8x10 inches would be available.