CityZen is a rather aged bit of software and doesn't run well on PalmOS devices manufactured in the 21st century.
As such, it is no longer officially supported. Recompiling it for modern devices is not a trivial matter as it does all sorts of horrible non-standard things based on assumptions about the hardware inside old Palm machines. These assumptions are no longer true which is why it won't run on modern devices.
I am considering producing an updated version to take advantages of the increased power of todays devices. Possible features would include a proper spherical projection, coloured maps and the ability to add customised overlays.
A while ago, I built a prototype system to explore how much processing power would be required to handle drawing a true spherical projection akin to a real atlas. Assuming you have the appropriate Java technology in your web browser, you can play with it here.
In order to produce something like this for PalmOS systems, I would of course need a shiny new fangled handheld machine. If you want to give one to me, let me know!