Check out the "Norton Scrapbook" it's $15 including shipping from www.ClassicBikeBooks.com they may also have the Norton Portfolio as well as classic bike magazines from the UK. Very good folks and service is first class.
Certainly there must be more world wide magazine articles in 1975 about the Norton Mk3!
This list of 5 is from Old Britts.
Norton 850 John Player Special: Cycle Test, Cycle - Dec 1975
Norton Commando Mk 3: 10,000 km Test, Motorcycling Monthly - Nov 1975
The Cleancut Commando, Two Wheels - Oct 1975
Norton 850 Commando: Road Test, Cycle World - Dec 1975
Norton Commando Mk 3 Motorcycling Monthly - Dec 1975
Two Wheels magazine is apparently Australia.
Cycle, Cycle World is USA.
Motorcycling Monthly what country?