How to get/find the terminal adapters for the MPI400 ?

The MPI400 uses the green Phoenix Contact terminal adapters.

On the device backside you have one 2 pin , one 3 pin, one 5 pin and one 6 pin connector.
Here is the link to the 3 pin adapter from the manufacturer:

https://www.phoenixcontact.com/en-us/products/pcb-plug-mc-15-3-st-35-1840379

Instead of the 6 pin connector you could even use e.g. 2 * 3 pin connectors to be more flexible.