Model 200 RAM
The model 200 comes with 24k built in, and supports up to 2 more banks of 24k in the form of ceramic dip modules that plug into the Option RAM #1 & #2 sockets.
The original 24K module was Catalog Number 26-3866.
Here is an open source design for a new compatible module. Actually it's a few different varaitions of modules to suit different chips availability, and different user skill at hand soldering.
This is new and not yet tested, but the circuit is simple.
https://github.com/bkw777/TANDY_200_RAM
More info