OK so I visited the Forbidden zone, and need key to access. I went back to the Think Tank and spoke to all the drs about Moibus and the Forbidden Zone, but yet no key?

You can't enter the Forbidden Zone Dome until you begin the final end game sequence. You obtain it via quests. Once everything for the Think Tanks is done, you speak to Dr.Klein who says you have everything you need to bypass security.

But don't worry, it's not like in FNV when you can't go in and out of it. You enter the dome but it doesn't restrain you from exploring further. You can go in and out as you please.

Thanks, just finished the X13 - Stealth quest so maybe it will open up now.