For some reason I cannot build an MCC in the later stages of the ED campaign. I got the message that I was trusted to use nuclear weapons 27 days before the Earth is supposed to collapse into the sun. When I click on the Gruz and on the tabs, I don't see the MCC center there. Do I need to research missiles first?

I'm pretty sure you need the ballistic missile launcher tech researched to build the missile control center... if not the nuclear missile as well. I don't like the MCC much, tbh, because it's too costly to use: 1 MCC + 1 silo costs 3000, and each nuclear missile costs 5000.