First of all Peter, may I welcome you to the Forum and hope that you will visit often.
On the subject of your post, Nienburg, we have very little in comparison to other BAOR locations (but more than some others it must be said), so it might be a little difficult to find any great detail at this time.
That said, have you tried the 24 Missile Regiment RA website? Take a look at the "Links" page on the main site.
Also, 21 Engineer Regiment RE were in Nienburg in various forms and names for a long period of time from the 1950's. It could be worth a try contacting the RE Museum to see if they might help. There are also a number of ex-RE members on the Forum who might be able to make better suggestions than I can though.
Conversely, anything you may be able to tell
us about Nienburg will be most welcome, however small you may take it to be. For example, were the Barracks new, or were they there before with another name?
Now, in my best Babel Fish German
Es nimmt viele Stücke, um ein Puzzlespiel, Peter abzuschließen.