There are already many holders available, but I couldn't find one for the cities and towns I printed out. I made a simple holder in which the pieces fit. 

You can of course print the holders in different colors for the various players. 

The holder is intended for the pieces that you can print at:

https://www.instructables.com/3D-Catan-Designed-3D-Printed-and-Painted/ 
or
https://www.printables.com/model/383376-3d-catan