The first of the slim tiles have been uploaded to the March product folder. There's also a new set of floor tools that will allow you to put together custom configurations of slim tiles.
Using something like 3D Builder you can open up a tool and any combination of slim tiles. Space out the tiles 38.1mm around the tool then combine and save out your custom tile.
The tool is there to delete any of the redundant clip holes and join the tiles together cleanly. I'll be doing a step by step guide for this once I'm finished up with Marches models