The earliest pure "Luger" book that I can think of is Fred Datig's "The Luger Pistol" first published in 1955 followed closely by Harry Jones' "Luger Variations" in 1959. Charlie Kenyon's classic "Lugers at Random" didn't show up until 10 years later.
At a quick count, I have around 50 books/publications devoted to the Luger with 5 different languages represented (four of which I can read with varying degrees of difficulty
). I have close to double that amount of books on semi-auto pistols and firearms in general, most of which have references to the Luger.
In the garage I have easily 200-250 magagazines/publications (gun magazines, AUTOMAG, etc.) that contain Luger information, and a bunch of old Luger catalogs/listings from Shattuck, Drollinger, Bessler and others (unfortunately I have disposed of a lot of the catalogs that I had...just ran out of room). You pick up a lot of "stuff" in 50 years.