You came to the right place to ask this question.
While I can't speak for Neumann or AKG, I can definitely talk about them! I too had wondered the same question you asked, fortunately, I was able to answer by starting a microphone company to fill that need.
Neumann for many years made great mics, they may still but they are not the same as what they used to do, they are different kinds of mics now.
AKG has been on a steady decline (in terms of high end studio mics)for MANY years thier current position is no real surprise, I think thier primary business is oem headsets etc.
Studio mics is like the studio business, largely glamour driven, difficult to make huge corporate sized profits in.
Recreating items from the past is a GIANT pain in the ass. To really clone parts requires custom machining, given the relatively small volume of high end mics sales makes the parts cost alot. For example, people have been asking me for years to recreate the KM54, and when I reply that it would cost $2000 or more, they change thier minds. So to really recreate old mics sometimes doesn't make sense, even the customer that asked for it doesn't want it!
Recreating the original tone, well, a part that has been aged 30 years will sound different than one that hasn't, and who really knows what that mic sounded like 30 years ago anyway?
On the other hand, there are some people who are doing what you are looking for.
CHEERS!