Sadly, the kind of guys you are looking for are either dying off or retiring. Terry Brewer was a British Diplomat who was also involved in clandestine activities; he gave tours for years, but he retired in 2012 and sadly passed away soon after his retirement. The guides at the company he founded still share some of his stories. Richard Campbell worked for the US government in Germany for 50 years (mostly in Berlin) in a variety of activities (including clandestine ones) and later became the guide for US government VIPs in Berlin (including 3 Presidents); he stopped giving tours in 2016. I got to tour with the latter, but not the former.
I have had two very memorable guides through Context Travel who were willing to share their experience of growing up in East Germany (the DDR) and of the fall of the Berlin Wall. One was Chris Benedict, who was an 11-yr-old living in a committed communist family when the wall fell. The other was Robert Sommer, who was the 15-year-old son of an East German bureaucrat and was starting to fall into the DDR music counterculture scene when the wall fell. Tours with both were pretty fascinating, but Context is definitely on the pricey side. Context will, however, allow you to make tours contingent on getting the guide you would like to have. When I googled Robert's name to make sure I was giving the right spelling, I saw a glowing review for him in the context of the Berlin Expert tour company. I'm not sure what the rates are there.