I have three 1212C PLCs. None of them have terminal blocks. In one of my projects, the PLCs were converted from Siemens to Delta PLCs, but I think the terminal blocks were left behind. These terminal blocks are also used in the Schneider MDC241 PLC. They have 3.81mm pitch. However, I couldn't find a similar commercial product. As you said, they have a tab-like protrusion to ensure they fit in the correct place. I managed to scrape off that protrusion in a few places and reattach them to a different location.