Interesting. I see that it comes with 12 slides for each month of the year. Not sure it would be easy to find though.
I have two of those, the earlier monochrome and later color version. They're invaluable to me as I don't use a computer at my radio desk (I'm very old school). The early one came with an overlay for the Great Cirlce path at 40* North, but now I live at 25* N so...
They turn up on eBay from time to time. Not expensive.